The performance optimization of the front-end mobile terminal needs to be based on the characteristics of the mobile terminal. 1. Reduce the number of requests and resource volume of the first screen, including merging JS/CSS files, using on-demand loading, compressing pictures and selecting appropriate formats; 2. Use caching strategies to reduce duplicate loading, such as setting up HTTP cache headers, using Service Worker to pre-cache, and locally storing interface data; 3. Optimizing rendering performance and interactive experience, avoiding forced synchronization of layouts and long tasks, simplifying page structure, and delaying non-critical animations; 4. Use lightweight frameworks and modern features, such as choosing Preact/Svelte, enabling Tree Shaking, using native APIs, enabling HTTP/2 and Brotli compression.

The performance optimization of the front-end mobile terminal is actually very different from that of the PC terminal, especially in terms of network, device capabilities and user habits. To truly improve the experience of mobile users, we cannot rely solely on "general routines" such as compressing codes and lazy loading of pictures, but also consider the unique restrictions and usage scenarios of the mobile terminal.

The following aspects are relatively critical optimization points in actual development and can solve many real problems.

Reduce the number of requests and resource volume on the first screen

The network environment of mobile users is unstable and the traffic is limited, so controlling the number of requests and resource sizes loaded on the first screen is particularly important.

• Merge JS/CSS files : Although modern packaging tools will do code segmentation by default, for mobile devices, sometimes "small points" are better.
• Use on-demand loading : for example, route-level lazy loading, or component-level dynamic imports to avoid loading a bunch of unused code from the beginning.
• Compress pictures and choose the right format : WebP is a good choice, which saves more traffic than JPEG/PNG and has good quality. Don't forget to set the appropriate width and height to avoid wasting bandwidth to load large images and then zoom in.

For example, if a page is loaded with more than 10 JS files and a bunch of images, it may take several seconds to start rendering on a 3G network. But if the key CSS is inlined and JS is merged into one or two files, the loading speed can be significantly improved.

Reduce duplicate loading with caching strategies

Mobile users often open the same website at different times. Reasonable use of cache can greatly reduce the amount of repeated downloads.

• The HTTP cache header is properly set : For long-term unchanged static resources (such as fonts, pictures, and third-party libraries), set a long cache such as Cache-Control: max-age=31536000 .
• Service Worker Pre-cache Key Resources : You can access some page content offline, and speed up the speed of secondary access.
• Local storage cached data interface response : For example, some configuration information or user status can be present in localStorage or IndexedDB to avoid re-pulling every time.

Note that the cache strategy is not the longer the better, especially for content that is updated frequently. It needs to be flexibly set according to the resource type.

Optimize rendering performance and interactive experience

The performance of mobile browsers is not as good as that of desktop, and animations and complex layouts are prone to lag, affecting the user experience.

• Avoid forced synchronization of layout and long tasks : For example, when operating the DOM frequently, try to use requestAnimationFrame or batch processing.
• Simplify page structure : Don’t have too deep CSS levels to reduce the cost of rearranged redrawing.
• Delayed non-critical animations/special effects : For example, the animation effect that is played before scrolling to the bottom, you can wait until the main content is rendered before loading the relevant scripts.

In addition, there are many touch interactions on the mobile terminal, so you should pay attention to preventing too many events from bubbled, resulting in performance degradation, and avoid unnecessary listener binding.

Use lightweight frames and modern features

There are now many frameworks and tools that are optimized for mobile terminals, such as Preact and Svelte. They are smaller in size and faster in operation, making them suitable for mobile projects.

• Enable Tree Shaking and Dead Code Elimination : Make sure that the final packaged code is the most streamlined.
• Use native APIs to replace compatibility libraries : for example, use IntersectionObserver to implement lazy loading instead of relying on jQuery plug-in.
• Turn on HTTP/2 and Brotli compression : the transmission efficiency is higher, especially for mobile devices, saving traffic and speeding up.

Of course, if your project has used mainstream frameworks such as React/Vue, it does not have to be replaced, but can be optimized through code splitting, loading on demand, etc.

Basically that's it. Mobile performance optimization is not a high-tech, but every detail is worth taking seriously. Doing well will not only allow users to see content faster, but also reduce bounce rates and improve the overall experience.

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