{"id":100468,"date":"2025-07-04T18:45:45","date_gmt":"2025-07-04T13:15:45","guid":{"rendered":"https:\/\/www.admecindia.co.in\/?p=100468"},"modified":"2025-07-28T12:32:59","modified_gmt":"2025-07-28T07:02:59","slug":"latest-javascript-mistakes-by-beginners","status":"publish","type":"post","link":"https:\/\/www.admecindia.co.in\/web-design\/latest-javascript-mistakes-by-beginners\/","title":{"rendered":"Latest JavaScript Mistakes by Beginners"},"content":{"rendered":"<div id=\"bsf_rt_marker\"><\/div>\n<p>Continuously JavaScript is in high demand by all <strong>types of programmers<\/strong>. Its high demand has encouraged many programmers and students to learn it. Most of them are not adequately trained by any training institute. Rather, they learned on their own without any proper guidance or evaluation. It has increased errors in JavaScript code.<\/p>\n\n\n\n<p>In this blog, we\u2019ll discuss the <strong>most common JavaScript mistakes made by developers<\/strong>. It will further help new developers to avoid and solve such errors. Let\u2019s make sure that your <strong><a href=\"https:\/\/www.admecindia.co.in\/course\/best-javascript-master-course\/\" target=\"_blank\" rel=\"noreferrer noopener\">JavaScript training path<\/a><\/strong> is smoother and your code is cleaner.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Latest JavaScript Mistakes Made by Developers<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"569\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=1024%2C569&#038;ssl=1\" alt=\"Advanced JavaScript Training by Professionals in Delhi\" class=\"wp-image-13448\" srcset=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=1024%2C569&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=300%2C167&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=768%2C427&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=1536%2C854&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?resize=900%2C500&amp;ssl=1 900w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2014\/01\/admec-internal-banner-advanced-javascript-training-by-professionals-in-delhi.jpg?w=2000&amp;ssl=1 2000w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<div style=\"height:33px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h3 class=\"wp-block-heading\">Mistake #1 &#8211; Using var too much instead of let and const<\/h3>\n\n\n\n<p>One of the most common mistakes is using <strong>\u201cvar\u201d to declare variables<\/strong>. While \u201cvar\u201d can lead to unexpected behavior due to its function scope. This can cause bugs that are hard to track, especially in larger projects.<\/p>\n\n\n\n<p>For example, when a variable is declared with \u201cvar\u201d inside a loop, it gets hoisted (i.e., moved to the top of its function scope), which can create confusion about its value.<\/p>\n\n\n\n<p>Here\u2019s what can go wrong with \u201cvar\u201d:<\/p>\n\n\n\n<p><strong>Example:<\/strong><\/p>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>for (var i = 0; i &lt; 3; i++){\n    setTimeout(function(){\n      console.log(i);\n      document.writeln(i);\n    }, 1000);\n}<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #C586C0\">for<\/span><span style=\"color: #D4D4D4\"> (<\/span><span style=\"color: #569CD6\">var<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #B5CEA8\">0<\/span><span style=\"color: #D4D4D4\">; <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\"> &lt; <\/span><span style=\"color: #B5CEA8\">3<\/span><span style=\"color: #D4D4D4\">; <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">++){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\">(){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"195\" height=\"102\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output.jpg?resize=195%2C102&#038;ssl=1\" alt=\"Output\" class=\"wp-image-100469\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>In this example, \u201cvar\u201d causes the loop variable \u2018i\u2019 to be shared across all iterations, resulting in \u2018i\u2019 beginning \u20183\u2019 when the \u201csetTimeout()\u201d callback executes.<\/p>\n\n\n\n<p><strong>The Solution:<\/strong><\/p>\n\n\n\n<p>Instead of \u201cvar\u201d, use \u201clet\u201d or \u201cconst\u201d:<br>\u2022 \u201clet\u201d has block scope and is perfect for variables whose value might change.<br>\u2022 \u201cconst\u201d also has block scope but is used when the variable\u2019s value shouldn\u2019t change.<br>Now let\u2019s fix this with \u201clet\u201d:<\/p>\n\n\n\n<p><strong>Example<\/strong>:<\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>for(let i = 0; i &lt; 3; i++){\n  setTimeout(function(){\n    console.log(i);\n    document.writeln(i);\n  }, 1000);\n}<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #C586C0\">for<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #569CD6\">let<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #B5CEA8\">0<\/span><span style=\"color: #D4D4D4\">; <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\"> &lt; <\/span><span style=\"color: #B5CEA8\">3<\/span><span style=\"color: #D4D4D4\">; <\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">++){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\">(){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">i<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"208\" height=\"91\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-2.jpg?resize=208%2C91&#038;ssl=1\" alt=\"Output-2\" class=\"wp-image-100470\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><br>By using \u201clet,\u201d each iteration will get its own scoped variable, and the output will just be as expected.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><br>Mistake #2 \u2013 Not Using Asynchronous Approach in JavaScript<\/h3>\n\n\n\n<p>JavaScript has <strong><a href=\"https:\/\/www.w3schools.com\/js\/js_asynchronous.asp\" target=\"_blank\" rel=\"noreferrer noopener\">asynchronous features<\/a><\/strong> like setTimeout(), promises, and API calls. Many beginners are either not aware or not comfortable with managing asynchronous code. It leads to callback hell or unhandled promise rejections. Callback hell is a situation when there are many unnecessary function callbacks in a code.<\/p>\n\n\n\n<p><strong>Example: Callback Hell<\/strong><\/p>\n\n\n\n<p><strong>Code:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>setTimeout(() => {\n  document.writeln(\"Task 1&lt;br>\");\n  setTimeout(() => {\n    document.writeln(\"Task 2&lt;br>\");\n    setTimeout(() => {\n      document.writeln(\"Task 3&lt;br>\");\n      setTimeout(() => {\n        document.writeln(\"Task 4&lt;br>\");\n        setTimeout(() => {\n          document.writeln(\"Task 5&lt;br>\");\n        }, 1000);\n      }, 1000);\n    }, 1000);\n  }, 1000);\n}, 1000);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 1&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 2&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 3&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">        <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 4&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">        <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">          <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 5&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">        }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  }, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"91\" height=\"162\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-3.jpg?resize=91%2C162&#038;ssl=1\" alt=\"Output-3\" class=\"wp-image-100471\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>It works for sure but once you add a few more tasks, the code turns into a tangled mess.<\/p>\n\n\n\n<p><strong>The Solution<\/strong><\/p>\n\n\n\n<p>Use promises or async\/await to handle asynchronous code in a cleaner and more readable way. This helps ensure that your code runs in the correct order and that errors are handled properly.<\/p>\n\n\n\n<p><strong>Example: A Cleaner Way \u2013 Using Promises with async\/await<\/strong><\/p>\n\n\n\n<p><strong>Code:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>function delayLog(message, time) {\n  return new Promise(resolve => {\n    setTimeout(() => {\n      document.writeln(message);\n      resolve();\n    }, time);\n });\n \n async function runTasks() {\n   await delayLog(\"Task 1&lt;br>\", 1000);\n   await delayLog(\"Task 2&lt;br>\", 1000);\n   await delayLog(\"Task 3&lt;br>\", 1000);\n   await delayLog(\"Task 4&lt;br>\", 1000);\n   await delayLog(\"Task 5&lt;br>\", 1000);\n }\n runTasks();<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">message<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #9CDCFE\">time<\/span><span style=\"color: #D4D4D4\">) {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #C586C0\">return<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">new<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4EC9B0\">Promise<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">resolve<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">message<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">      <\/span><span style=\"color: #DCDCAA\">resolve<\/span><span style=\"color: #D4D4D4\">();<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    }, <\/span><span style=\"color: #9CDCFE\">time<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\"> });<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\"> <\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">async<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">runTasks<\/span><span style=\"color: #D4D4D4\">() {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">   <\/span><span style=\"color: #C586C0\">await<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 1&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">   <\/span><span style=\"color: #C586C0\">await<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 2&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">   <\/span><span style=\"color: #C586C0\">await<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 3&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">   <\/span><span style=\"color: #C586C0\">await<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 4&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">   <\/span><span style=\"color: #C586C0\">await<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">delayLog<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Task 5&lt;br&gt;&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\"> }<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #DCDCAA\">runTasks<\/span><span style=\"color: #D4D4D4\">();<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"91\" height=\"162\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-4.jpg?resize=91%2C162&#038;ssl=1\" alt=\"Output-4\" class=\"wp-image-100474\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>With this structure, the same logic becomes much easier to read, manage, and modify.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Mistake #3 &#8211; Confusing \u201c==\u201d with \u201c===\u201d<br><\/h3>\n\n\n\n<p>A common trap many beginners fall into is using the wrong equality operator. In JavaScript, there are two ways to check if values are equal: == and ===. At first, they look similar but they behave differently. \u201c==\u201d (equality) tries to be smart by changing the types of the values to match before comparing.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u201c===\u201d (strict equality) doesn\u2019t change anything, it checks both the value and the type exactly as they are<\/li>\n\n\n\n<li>This small difference can cause bugs that are hard to track down later<\/li>\n<\/ul>\n\n\n\n<p><strong>Example:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>console.log(5 == '5');   \/\/ true - because '5' is converted to number&lt;br>\nconsole.log(5 === '5');  \/\/ false - both are different type: number vs string<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #B5CEA8\">5<\/span><span style=\"color: #D4D4D4\"> == <\/span><span style=\"color: #CE9178\">&#39;5&#39;<\/span><span style=\"color: #D4D4D4\">);   <\/span><span style=\"color: #6A9955\">\/\/ true - because &#39;5&#39; is converted to number&lt;br&gt;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #B5CEA8\">5<\/span><span style=\"color: #D4D4D4\"> === <\/span><span style=\"color: #CE9178\">&#39;5&#39;<\/span><span style=\"color: #D4D4D4\">);  <\/span><span style=\"color: #6A9955\">\/\/ false - both are different type: number vs string<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Why it matters:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>If you\u2019re not careful using \u201c==\u201d might make your code behave in ways you didn\u2019t intend.<\/li>\n\n\n\n<li> For example, Code:<\/li>\n<\/ul>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>if ('0' == false) {\n  document.write(\"This runs!\");\n}<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #C586C0\">if<\/span><span style=\"color: #D4D4D4\"> (<\/span><span style=\"color: #CE9178\">&#39;0&#39;<\/span><span style=\"color: #D4D4D4\"> == <\/span><span style=\"color: #569CD6\">false<\/span><span style=\"color: #D4D4D4\">) {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">write<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;This runs!&quot;<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"128\" height=\"35\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-5.jpg?resize=128%2C35&#038;ssl=1\" alt=\"Output 5\" class=\"wp-image-100475\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<ul class=\"wp-block-list\">\n<li>This prints \u201cThis runs!\u201d, which is often not what you want because \u20180\u2019 is converted to false.<\/li>\n<\/ul>\n\n\n\n<p><strong>The Solution:<\/strong><\/p>\n\n\n\n<p>To stay safe and avoid bugs, always use \u201c===\u201d and \u201c!==\u201d unless you have a very specific reason not to. It\u2019s a good habit that keeps your comparisons predictable and your code more reliable.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Mistake #4 &#8211; Misunderstanding Variable Scope<br><\/h3>\n\n\n\n<p>Many beginners don\u2019t realize that where you declare a variable matters a lot in JavaScript. If you use \u201cvar\u201d, the variable function-scoped is not block-scoped. That means it doesn\u2019t behave the way you might expect inside blocks like if statements or loops. This often leads to bugs that are super confusing to track down.<\/p>\n\n\n\n<p><strong>Example code:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>if (true) {\n  var name = \"John\";\n  document.writeln(name); \/\/ Output: John\n}<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #C586C0\">if<\/span><span style=\"color: #D4D4D4\"> (<\/span><span style=\"color: #569CD6\">true<\/span><span style=\"color: #D4D4D4\">) {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #569CD6\">var<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #9CDCFE\">name<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #CE9178\">&quot;John&quot;<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">name<\/span><span style=\"color: #D4D4D4\">); <\/span><span style=\"color: #6A9955\">\/\/ Output: John<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"63\" height=\"31\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-6.jpg?resize=63%2C31&#038;ssl=1\" alt=\"Output-6\" class=\"wp-image-100476\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Even though the name variable was declared inside the if block, it still exists outside of it!<\/p>\n\n\n\n<p><strong>The Solution:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Prefer using let and const, instead of var.<\/li>\n\n\n\n<li>\u201clet\u201d allows to reassign values but keeps the scope inside the block {}.<\/li>\n\n\n\n<li>\u201cconst\u201d keeps the value constant and also block-scoped.<\/li>\n<\/ul>\n\n\n\n<p>Example with let, Code:<\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>if (true) {\n  let city = \"New Delhi\";\n}\nconsole.log(city);  \/\/ Reference error<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #C586C0\">if<\/span><span style=\"color: #D4D4D4\"> (<\/span><span style=\"color: #569CD6\">true<\/span><span style=\"color: #D4D4D4\">) {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #569CD6\">let<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #9CDCFE\">city<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #CE9178\">&quot;New Delhi&quot;<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">}<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">city<\/span><span style=\"color: #D4D4D4\">);  <\/span><span style=\"color: #6A9955\">\/\/ Reference error<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"360\" height=\"88\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-7.jpg?resize=360%2C88&#038;ssl=1\" alt=\"Output-7\" class=\"wp-image-100477\" srcset=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-7.jpg?w=360&amp;ssl=1 360w, https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-7.jpg?resize=300%2C73&amp;ssl=1 300w\" sizes=\"auto, (max-width: 360px) 100vw, 360px\" \/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Now, the variable \u201ccity\u201d is safely locked inside the if block, exactly what you expect.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Mistake #5 &#8211; Not Understanding How \u201cthis\u201d Works in JavaScript<\/h3>\n\n\n\n<p>In JavaScript, the value of \u201cthis\u201d can change depending on how a function is called, not where it\u2019s written. Many beginners expect \u201cthis\u201d to always point to the object that contains the function. But that\u2019s not always true, especially inside regular functions, event handlers, or when working with \u201csetTimeout\u201d. This leads to <strong>strange, unexpected bugs<\/strong>.<\/p>\n\n\n\n<p><strong>Example, Code:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const user = {\n  username: \"Alice\",\n  greet: function(){\n    document.writeln(\"Hello, \" + this.username);\n  }\n};\nsetTimeout(user.greet, 1000);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">user<\/span><span style=\"color: #D4D4D4\"> = {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">username:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #CE9178\">&quot;Alice&quot;<\/span><span style=\"color: #D4D4D4\">,<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #DCDCAA\">greet<\/span><span style=\"color: #9CDCFE\">:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\">(){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Hello, &quot;<\/span><span style=\"color: #D4D4D4\"> + <\/span><span style=\"color: #569CD6\">this<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">username<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  }<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">};<\/span><\/span>\n<span class=\"line\"><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">greet<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"200\" height=\"40\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-8.jpg?resize=200%2C40&#038;ssl=1\" alt=\"Output-8\" class=\"wp-image-100478\"\/><\/figure>\n\n\n\n<p>Wait, why undefined? Because when \u201csetTimeout\u201d calls \u201cuser.greet\u201d, it loses its original object reference, so \u201cthis\u201d becomes \u201cwindow\u201d (or \u201cundefined\u201d in strict mode).<\/p>\n\n\n\n<p><strong>The Solution:<\/strong><\/p>\n\n\n\n<p>Use an arrow function \u201c()=&gt;{}\u201d or explicitly bind \u201cthis\u201d to the correct object.<\/p>\n\n\n\n<p><strong>Example 1 (Arrow function fix),<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const user = {\n  username: \"Alice\",\n  greet: function(){\n    document.writeln(\"Hello, \" + this.username);\n  }\n};\nsetTimeout(() => user.greet(), 1000);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">user<\/span><span style=\"color: #D4D4D4\"> = {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">username:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #CE9178\">&quot;Alice&quot;<\/span><span style=\"color: #D4D4D4\">,<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #DCDCAA\">greet<\/span><span style=\"color: #9CDCFE\">:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\">(){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Hello, &quot;<\/span><span style=\"color: #D4D4D4\"> + <\/span><span style=\"color: #569CD6\">this<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">username<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  }<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">};<\/span><\/span>\n<span class=\"line\"><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(() <\/span><span style=\"color: #569CD6\">=&gt;<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">greet<\/span><span style=\"color: #D4D4D4\">(), <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"149\" height=\"35\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-9.jpg?resize=149%2C35&#038;ssl=1\" alt=\"Output 9\" class=\"wp-image-100479\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Example 1 (bind fix),<\/strong><\/p>\n\n\n\n<p><strong>Code:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const user = {\n  username: \"Alice\",\n  greet: function(){\n    document.writeln(\"Hello, \" + this.username);\n  }\n};\n\nsetTimeout(user.greet.bind(user), 1000);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">user<\/span><span style=\"color: #D4D4D4\"> = {<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #9CDCFE\">username:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #CE9178\">&quot;Alice&quot;<\/span><span style=\"color: #D4D4D4\">,<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  <\/span><span style=\"color: #DCDCAA\">greet<\/span><span style=\"color: #9CDCFE\">:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #569CD6\">function<\/span><span style=\"color: #D4D4D4\">(){<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">    <\/span><span style=\"color: #9CDCFE\">document<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">writeln<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #CE9178\">&quot;Hello, &quot;<\/span><span style=\"color: #D4D4D4\"> + <\/span><span style=\"color: #569CD6\">this<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">username<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">  }<\/span><\/span>\n<span class=\"line\"><span style=\"color: #D4D4D4\">};<\/span><\/span>\n<span class=\"line\"><\/span>\n<span class=\"line\"><span style=\"color: #DCDCAA\">setTimeout<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">greet<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">bind<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">), <\/span><span style=\"color: #B5CEA8\">1000<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"149\" height=\"35\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/Output-11.jpg?resize=149%2C35&#038;ssl=1\" alt=\"Output- 11\" class=\"wp-image-100480\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Now, \u201cthis\u201d stays linked to a user, you\u2019ll get \u201cHello, Alice\u201d as expected.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Mistake #6 &#8211; Modifying Objects or Arrays Directly Without Cloning<\/h3>\n\n\n\n<p>In JavaScript, <strong><a href=\"https:\/\/www.admecindia.co.in\/web-design\/data-structure-in-javascript\/\" target=\"_blank\" rel=\"noreferrer noopener\">data structures<\/a><\/strong> like <strong>Arrays and <a href=\"https:\/\/www.admecindia.co.in\/web-design\/javascript-objects-complete-guide\/\">Objects<\/a><\/strong> are reference types. That means, when you assign an object or array to a new variable, you\u2019re not creating a new copy, you\u2019re just pointing to the same thing in the memory. Beginners often change the new variable thinking it\u2019s a separate copy. But they\u2019re changing the original data too, sometimes causing huge, hidden bugs in applications.<\/p>\n\n\n\n<p><strong>Example code for Arrays:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const originalArray = &#91;1, 2, 3&#93;;\nconst newArray = originalArray;\nnewArray.push(4);\nconsole.log(originalArray);\nconsole.log(newArray);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">originalArray<\/span><span style=\"color: #D4D4D4\"> = &#91;<\/span><span style=\"color: #B5CEA8\">1<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">2<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">3<\/span><span style=\"color: #D4D4D4\">&#93;;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">newArray<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #9CDCFE\">originalArray<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">newArray<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">push<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #B5CEA8\">4<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">originalArray<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">newArray<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"204\" height=\"75\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/output-12.jpg?resize=204%2C75&#038;ssl=1\" alt=\"\" class=\"wp-image-100481\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Example code for objects<\/strong>:<\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const user = { name: \"Alice\", age: 25 };\nconst copiedUser = user;\ncopiedUser.age = 30;\nconsole.log(user.age);\nconsole.log(copiedUser.age);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">user<\/span><span style=\"color: #D4D4D4\"> = { <\/span><span style=\"color: #9CDCFE\">name:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #CE9178\">&quot;Alice&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #9CDCFE\">age:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #B5CEA8\">25<\/span><span style=\"color: #D4D4D4\"> };<\/span><\/span>\n<span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">copiedUser<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">copiedUser<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #B5CEA8\">30<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">copiedUser<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"36\" height=\"64\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/output-13.jpg?resize=36%2C64&#038;ssl=1\" alt=\"output 13\" class=\"wp-image-100482\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Notice how \u201coriginalArray\u201d also changed, even though we only pushed (4) to \u201cnewArray\u201d? That\u2019s because both variables are pointing to the same array.<\/p>\n\n\n\n<p><strong>The Solution:<\/strong><\/p>\n\n\n\n<p>Always clone the array or object if you want a real copy before modifying it.<\/p>\n\n\n\n<p><strong>Example<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const originalArray = &#91;1, 2, 3&#93;;\nconst newArray = &#91;...originalArray&#93;;\nnewArray.push(4);\nconsole.log(originalArray);\nconsole.log(newArray);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">originalArray<\/span><span style=\"color: #D4D4D4\"> = &#91;<\/span><span style=\"color: #B5CEA8\">1<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">2<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #B5CEA8\">3<\/span><span style=\"color: #D4D4D4\">&#93;;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">newArray<\/span><span style=\"color: #D4D4D4\"> = &#91;...<\/span><span style=\"color: #9CDCFE\">originalArray<\/span><span style=\"color: #D4D4D4\">&#93;;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">newArray<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">push<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #B5CEA8\">4<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">originalArray<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">newArray<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"202\" height=\"75\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/output-14.jpg?resize=202%2C75&#038;ssl=1\" alt=\"output 14\" class=\"wp-image-100484\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Example:<\/strong><\/p>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<div class=\"wp-block-kevinbatdorf-code-block-pro\" data-code-block-pro-font-family=\"Code-Pro-JetBrains-Mono\" style=\"font-size:.875rem;font-family:Code-Pro-JetBrains-Mono,ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,monospace;line-height:1.25rem;--cbp-tab-width:2;tab-size:var(--cbp-tab-width, 2)\"><span style=\"display:block;padding:16px 0 0 16px;margin-bottom:-1px;width:100%;text-align:left;background-color:#1E1E1E\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"54\" height=\"14\" viewBox=\"0 0 54 14\"><g fill=\"none\" fill-rule=\"evenodd\" transform=\"translate(1 1)\"><circle cx=\"6\" cy=\"6\" r=\"6\" fill=\"#FF5F56\" stroke=\"#E0443E\" stroke-width=\".5\"><\/circle><circle cx=\"26\" cy=\"6\" r=\"6\" fill=\"#FFBD2E\" stroke=\"#DEA123\" stroke-width=\".5\"><\/circle><circle cx=\"46\" cy=\"6\" r=\"6\" fill=\"#27C93F\" stroke=\"#1AAB29\" stroke-width=\".5\"><\/circle><\/g><\/svg><\/span><span role=\"button\" tabindex=\"0\" style=\"color:#D4D4D4;display:none\" aria-label=\"Copy\" class=\"code-block-pro-copy-button\"><pre class=\"code-block-pro-copy-button-pre\" aria-hidden=\"true\"><textarea class=\"code-block-pro-copy-button-textarea\" tabindex=\"-1\" aria-hidden=\"true\" readonly>const user = { name: \"Alice\", age: 25 };\nconst copiedUser = { ...user };\ncopiedUser.age = 30;\nconsole.log(user.age);\nconsole.log(copiedUser.age);<\/textarea><\/pre><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" style=\"width:24px;height:24px\" fill=\"none\" viewBox=\"0 0 24 24\" stroke=\"currentColor\" stroke-width=\"2\"><path class=\"with-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4\"><\/path><path class=\"without-check\" stroke-linecap=\"round\" stroke-linejoin=\"round\" d=\"M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2\"><\/path><\/svg><\/span><pre class=\"shiki dark-plus\" style=\"background-color: #1E1E1E\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">user<\/span><span style=\"color: #D4D4D4\"> = { <\/span><span style=\"color: #9CDCFE\">name:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #CE9178\">&quot;Alice&quot;<\/span><span style=\"color: #D4D4D4\">, <\/span><span style=\"color: #9CDCFE\">age:<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #B5CEA8\">25<\/span><span style=\"color: #D4D4D4\"> };<\/span><\/span>\n<span class=\"line\"><span style=\"color: #569CD6\">const<\/span><span style=\"color: #D4D4D4\"> <\/span><span style=\"color: #4FC1FF\">copiedUser<\/span><span style=\"color: #D4D4D4\"> = { ...<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\"> };<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">copiedUser<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\"> = <\/span><span style=\"color: #B5CEA8\">30<\/span><span style=\"color: #D4D4D4\">;<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">user<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span>\n<span class=\"line\"><span style=\"color: #9CDCFE\">console<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #DCDCAA\">log<\/span><span style=\"color: #D4D4D4\">(<\/span><span style=\"color: #9CDCFE\">copiedUser<\/span><span style=\"color: #D4D4D4\">.<\/span><span style=\"color: #9CDCFE\">age<\/span><span style=\"color: #D4D4D4\">);<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><strong>Output:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"36\" height=\"64\" src=\"https:\/\/i0.wp.com\/www.admecindia.co.in\/wp-content\/uploads\/2025\/07\/output-16.jpg?resize=36%2C64&#038;ssl=1\" alt=\"output- 16\" class=\"wp-image-100483\"\/><\/figure>\n\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Using the spread operator (\u2026) is a super clean way to make shallow copies.<\/p>\n\n\n\n<p>Helps prevent data mutation bugs that are very hard to debug later.<\/p>\n\n\n\n<p><strong>Conclusion<\/strong><\/p>\n\n\n\n<p>These 6 mistakes of JavaScript are game changers if a JavaScript developer like you follows them. You will be able to write bug-free code which offers great performance. Above given points don\u2019t just make you better at JavaScript\u2014they give you a unique way to solve such problems. This way, you can <strong><a href=\"https:\/\/www.admecindia.co.in\/courses\/web-designing-courses\/\" target=\"_blank\" rel=\"noreferrer noopener\">enhance your career in web design easily<\/a><\/strong>.<\/p>\n\n\n\n<p>Further, you can explore advanced options of JS with <a href=\"https:\/\/www.admecindia.co.in\/course\/advanced-javascript-master-plus-course\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>JavaScript 3 months master plus<\/strong> <\/a>and <strong><a href=\"https:\/\/www.admecindia.co.in\/course\/most-advanced-course-javascript-master-plus-plus\/\" target=\"_blank\" rel=\"noreferrer noopener\">4 months JS certificate course<\/a><\/strong>.<\/p>\n\n\n\n<p>You will get wonderful growth as a programmer with continuous practice and with proper approach. Keep reading similar blogs and apply these suggestions in your code. You will surely see a difference as a developer in you.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Continuously JavaScript is in high demand by all types of programmers. Its high demand has encouraged many programmers and students to learn it. Most of them are not adequately trained [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":13448,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[454,80],"tags":[102],"class_list":["post-100468","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-programming-languages","category-web-design","tag-javascript"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Latest JavaScript Mistakes by Beginners - ADMEC Multimedia Institute<\/title>\n<meta name=\"description\" content=\"Check out, what are the JavaScript mistakes usually done by beginner developers and find the right ways to improve your code.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.admecindia.co.in\/web-design\/latest-javascript-mistakes-by-beginners\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Latest JavaScript Mistakes by Beginners - 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