Code Splitting

May 20, 2023

Code splitting is a technique used in web development to reduce the initial load time of a web page by breaking the JavaScript code into smaller, more manageable chunks or modules. The purpose of code splitting is to improve the performance of web applications and enhance the user experience by delivering only the necessary code for a specific page or feature when it is needed.

How Code Splitting Works

In traditional web development, all the JavaScript code for a web application is bundled together and served to the client in a single file. This approach can lead to longer load times and slower performance, especially for larger applications. Code splitting, on the other hand, allows developers to split the JavaScript code into smaller, more focused modules that can be loaded on demand.

When a user visits a web page, only the code necessary to render that page is loaded initially. Additional modules are loaded asynchronously as the user interacts with the page, such as when they click on a button that triggers a new feature. This approach reduces the initial load time of the page and improves overall performance.

Benefits of Code Splitting

There are several benefits to using code splitting in web development:

  • Faster Load Times: Code splitting can significantly reduce the initial load time of a web page by only loading the necessary code. This can improve the user experience, especially for users with slower internet connections.

  • Improved Performance: By breaking the code into smaller, more focused modules, code splitting can improve the overall performance of a web application. As modules are loaded on demand, the application can respond more quickly to user interactions.

  • Better Code Management: Code splitting can make it easier to manage the codebase for a web application. By breaking the code into smaller modules, developers can more easily identify and fix issues, and can add new features more efficiently.

Code Splitting Techniques

There are several techniques that developers can use to implement code splitting in web applications:

1. Entry Points

One technique for code splitting is to define entry points in the codebase. An entry point is a module that represents a specific feature or page of the application. When the application is built, each entry point is compiled into a separate file, which can be loaded on demand.

For example, if a web application has three main features – a login page, a dashboard, and a settings page – each of these features could be defined as an entry point. When a user navigates to a specific page, only the code for that feature is loaded, rather than loading all the code for the entire application.

2. Dynamic Imports

Dynamic imports are another technique for code splitting in JavaScript. With dynamic imports, modules are only loaded when they are needed, rather than being loaded all at once.

To use dynamic imports, developers can create functions that load modules on demand. For example, if a web application includes a feature that only a small percentage of users will use, that feature’s module can be loaded dynamically when the user requests it, rather than being loaded on every page.

function loadModule() {
    .then((module) => {
      // Use the module
    .catch((err) => {
      // Handle errors

3. Code Splitting Libraries

There are also several libraries and tools available that can help developers implement code splitting in their web applications. These libraries can help automate the process of splitting the codebase into modules and loading them on demand.

One popular code splitting library is webpack, a module bundler for JavaScript applications. Webpack includes built-in support for code splitting and can automatically split the codebase into chunks based on entry points or other criteria.

Another library is Loadable Components, a library that simplifies the process of code splitting in React applications. Loadable Components allows developers to define components that are loaded on demand when they are needed, rather than being loaded all at once.

Best Practices for Code Splitting

While code splitting can offer significant benefits for web development, there are also some best practices that developers should follow to ensure that the implementation is effective and efficient:

  • Identify Entry Points: Before implementing code splitting, developers should identify the main entry points of the application, such as pages or features that are frequently used by users. These entry points can then be used to define the modules that should be loaded on demand.

  • Avoid Over-Splitting: While code splitting can improve performance, over-splitting the codebase can actually harm performance by increasing the number of requests needed to load the page. Developers should strike a balance between breaking the code into manageable modules and minimizing the number of requests needed.

  • Test Performance: Developers should test the performance of the application after implementing code splitting to ensure that it is delivering the expected benefits. Load testing and other performance testing techniques can help identify areas for improvement.