Code splitting is a front-end optimization technology that improves performance by splitting JS files and loading on demand. The core reason is to reduce initial loading time, avoid resource waste, and improve user experience. Implementation includes routing splitting, component lazy loading, dynamic import and Webpack magic annotations. Notes include splitting granularity, naming chunks, optimizing public dependencies, considering SEO influences and building tool characteristics. Mastering these key points can effectively apply code splitting in your project.
Code splitting is an optimization technology in front-end development. Its core purpose is to split a large JavaScript file into multiple small files and then load it on demand. The benefits of doing this are obvious: reduce initial loading time, improve page performance, and improve user experience.
Simply put, it does not load all the code from the beginning, but "load what is needed first, and talk about the others later."
Why do you need code splitting?
Modern web applications are becoming more and more complex. Without any optimization, the packaged JS files may be very large. For example, if you write a backend management system, the user needs to download all the code of the entire system when he accesses it for the first time, including the part that he will not use immediately, which is obviously unreasonable.
- The first screen loads slowly : users have to wait until the entire application is downloaded before they can see the content.
- Waste resources : Users may not access certain pages or feature modules at all.
- Impact experience : Especially when the mobile terminal or network is poor, the consequences are more obvious.
Therefore, code splitting is used to solve these problems - only load the corresponding code blocks when needed.
How to implement code splitting?
Currently, mainstream front-end frameworks and construction tools (such as React Webpack/Vite) have already supported code splitting well. The common practices are as follows:
- Routing-based splitting : Each page is individually packaged into a chunk.
- Lazy loading by component : Use
React.lazy
Suspense
to dynamically import components. - Dynamic import() : Manually control the asynchronous loading of a function or module.
- Webpack's magic comments : name the chunk for easy debugging and management.
For example, if you have a "Settings" page that does not need to load the relevant code before the user clicks to enter, you can write it like this:
const SettingsPage = React.lazy(() => import('./SettingsPage'));
In this way, Webpack will automatically split the component into an independent chunk and load it only when it is really needed.
Some details to pay attention to
Although code splitting is useful, it is not necessarily good if you just disassemble it. Some points you need to pay attention to:
- If you disassemble it too much, it will increase the number of HTTP requests, affecting the loading speed.
- Reasonably naming the chunk file will help to maintain and troubleshoot problems in the later stage.
- Using Webpack's
SplitChunksPlugin
can further optimize public dependencies. - It has a certain impact on SEO (because some of the content is loaded asynchronously), and pay special attention to it if it is an SSR or SSG project.
In addition, some tools like Vite do not actually do real code splitting in development mode, but only generate split files when building production versions, which is also misleading.
Let's summarize
The essence of code splitting is "loading on demand", which makes our applications start faster and run lighter. The implementation method is not difficult. The key is to understand when to disassemble, how to disassemble, and how to balance loading performance and code structure.
Basically all that is it. If you master these key points, you can use them in actual projects.
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