Downcodes editors bring you a practical guide on optimizing JavaScript files larger than 1MB. Large JS files will seriously affect web page loading speed and reduce user experience. This article will introduce in detail a variety of optimization methods, including code compression, code splitting, tree-shaking, CDN loading, lazy loading, asynchronous loading, etc., to help you improve web page performance.
JS files exceeding 1MB can be optimized and compressed through various methods such as code compression, code splitting, tree-shaking, using CDN to load third-party libraries, lazy loading or asynchronous loading. These technologies can significantly reduce JavaScript file size, speed up web page loading, improve user experience and improve SEO rankings.
Among these methods, code splitting is a particularly important strategy. Code splitting allows you to split a large JS file into multiple smaller files and load these files only when needed. The advantage of this is that it reduces the amount of data on the first page load, thus speeding up the loading of the page. Modern front-end build tools, such as Webpack and Rollup, provide easily configurable code splitting support.
Code compression is the most direct and common way to reduce JS file size. The compression process works by removing all unnecessary characters in the source code (such as spaces, newlines, and comments) and renaming variables to reduce the number of characters. This process does not change the results of the code.
Compression using tools and plugins: UglifyJS, Terser, and Google Closure Compiler are several popular JavaScript compression tools. Most modern front-end build tools (such as Webpack and Gulp) provide plugins or ways to integrate these compression tools. Automatic compression during the build process: Integrate compression steps into the automated build process to ensure that production code is always compressed. This avoids compression directly in the source code and keeps the source code readable and maintainable.Code splitting allows you to separate your code base into chunks and only load the corresponding chunks when actually needed. This is especially important for larger apps, as it can reduce the time it takes for the first screen to load.
Use module packaging tools such as Webpack: These tools provide simple configuration options to achieve code splitting. For example, Webpack implements dynamic import through the import() syntax, making it possible to load code on demand. Router-based splitting: For single page applications (SPA), route-based code splitting is very common. Dynamically load the script of the corresponding page according to the route visited by the user, reducing the initial loading of a large amount of useless code.Tree shaking is a technique that reduces the final file size by removing unused parts of the code. This requires the code to be modular and use ES Modules syntax, because this can be statically analyzed during the build process and determine which exports and imports are actually used.
Configure Webpack or Rollup for tree shaking: These tools often automatically enable tree shaking in production mode to help remove unused code. Be aware of code side effects: Avoid side effects when writing module code, as they may prevent tools from properly removing unused code.Using a CDN (Content Delivery Network) to load third-party libraries (such as jQuery, React, etc.) can reduce the load on the server and reduce the initial loading time of the application. This also means that users may load these libraries from cache, further reducing load times.
Choose a CDN with good caching: Some such as Google CDN or Cloudflare offer CDN services for multiple popular libraries. Comparing self-hosting vs. CDN hosting: Sometimes depending on the geographic location of your user base, self-hosting may be more conducive to control and performance optimization. Make your choice after weighing the pros and cons.Delaying or asynchronous loading of non-critical JavaScript code ensures that these codes do not block the rendering of the page. This approach is especially effective for features that are only required when the user interacts with them.
Utilizing async and defer attributes: HTML