How to Reduce Unused JavaScript in Your Code

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Cutting down on JavaScript is crucial for building modern websites. Reducing unused JavaScript significantly improves page performance and efficiency. As technology advances, the demand for faster and more efficient websites grows, making it essential to minimize JavaScript. This article provides tips to help you eliminate unnecessary JavaScript, enhancing your website’s speed and performance.

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Unused JavaScript, often called "dead code," refers to code in your web app that isn’t used but still exists in the JavaScript bundle sent to the browser. This idle code increases the bundle size, negatively impacting your website’s performance.

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1?.? ?D?e?v?e?l?o?p?m?e?n?t? ?R?e?s?i?d?u?e?:? During development, you might add code that becomes unnecessary later but forget to remove it. This can include unused functions, classes, or variables.

2?.? ?U?n?u?s?e?d? ?D?e?p?e?n?d?e?n?c?i?e?s?:? External JavaScript libraries may include their own unused code, adding extra weight to your project.

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Here are some methods to eliminate unused JavaScript from your web apps:

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Code splitting divides your JavaScript code into smaller chunks, which can be loaded on demand or simultaneously. This method reduces the need to load the entire JavaScript bundle every time, only loading what’s necessary.

For example, instead of a single large JavaScript file:

html

<script src="main.js"></script> <!-- 100kb file -->        

You can split it into smaller chunks:

html

<script async defer src="chunk1.js"></script> <!-- 30 kb file -->        

<script async defer src="chunk2.js"></script> <!-- 30 kb file -->        

<script async defer src="chunk3.js"></script> <!-- 30 kb file -->        

Many modern JavaScript frameworks, like Next.js or Vue, handle code splitting automatically, further optimizing the loading process.

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Tree shaking removes unused JavaScript, ensuring only necessary code is included in your bundle. Popular bundlers like Webpack, Rollup, or Vite use tree shaking to optimize JavaScript bundles.

To facilitate tree shaking, use modern ES6 syntax in your components:

javascript

// default import        

import Header from 'Components';        

// named import        

import { Header } from 'Components';        

// default export        

export default Header;        

// named export        

export { Header };        

This syntax helps the bundler identify and eliminate dead code.

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Minifying JavaScript involves removing unnecessary elements like whitespaces, comments, and syntax highlighting, resulting in a more compact and efficient bundle.

For example, before minification:

javascript

// multiply function        

const multiply = (a, b) => {        

  return a * b;        

}        

// call multiply function        

multiply(3, 4);        

After minification:        

javascript        

const multiply = (a, b) => a * b;        

multiply(3, 4);        

Tools like Terser, Uglify, and babel-minify can help with JavaScript minification.

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Loading JavaScript asynchronously prevents it from blocking the HTML parsing and rendering process. Use async and defer attributes in your script tags:

html

<script async defer src="main.js"></script>        

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ES6 modules allow dynamic imports, enabling you to load JavaScript modules based on specific conditions:

javascript

import('./helper.js')        

  .then((module) => {        

    // use helper code here        

  })        

  .catch((error) => {        

    // handle errors        

  });        

This approach ensures JavaScript bundles are only loaded when needed, optimizing performance.

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Lazy loading delays the loading of JavaScript modules until they are needed. This technique saves network bandwidth and improves performance. For instance, you can load JavaScript based on the viewport height, only fetching what’s visible on the screen.

Libraries are available to handle lazy loading for various elements, including images and videos, enhancing the user experience.

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This article explored six techniques to reduce unused JavaScript and boost your project’s performance. Each project is unique, so choose the methods that best suit your needs. Implementing these strategies allows you to build faster and more efficient websites and apps.

I am Furqan Hameed, a Software Engineer and Content Creator. If you have technical writing needs or any role inquiries, contact me on LinkedIn and follow me on LinkedIn.