How to set cache in css

In the process of website development, we often encounter a problem: the website access speed is impressive. Among them, an important factor is the cache settings of the website. In this article, I will introduce in detail the principles, methods, and optimization techniques of CSS caching.

1. Principle of Caching

The principle of website caching is very simple: save some commonly used files in the user’s local cache. The next time the user visits the same website, they can directly access it from Read files locally, resulting in faster loading.

CSS file is an important part of the website because it affects the appearance, interaction and other aspects of the website. When setting up the cache, we can use HTTP headers to specify a caching policy for a CSS file, allowing the browser to cache the file when it first accesses it, and then read it directly from the cache when accessing it again.

2. Cache setting method

The cache setting of CSS files mainly involves two HTTP headers: Expires and Cache-Control.

1. Expires

Expires is an HTTP header that is used to set the expiration time of the file. When setting this header, we can specify a fixed expiration time, such as Expires: Fri, 01 Jan 2022 00:00:00 GMT, or set a relative time, such as Expires: 1h.

When the client accesses the file for the first time, it will be cached and the cache expiration time will be saved locally. When the file is accessed again next time, the browser will determine whether the cache has expired. If it has not expired, the file will be read directly from the cache, otherwise the file will be requested again.

It should be noted that the Expires header depends on the client time. If the client time is inaccurate, the cache settings may be invalid.

2. Cache-Control

Compared with Expires, Cache-Control is more flexible. It is also an HTTP header whose value is a string containing multiple directives, such as Cache-Control: max-age=3600, public.

Some of the common directives include:

• max-age: Specifies the cache time of the file, in seconds.
• no-cache: Tell the client that it must first verify with the server whether the cache has expired.
• public: The file can be cached by public caches (such as CDNs).
• private: This file can only be cached by private caches, such as browser caches.

It should be noted that Cache-Control will override Expires.

3. Caching optimization techniques

1. Version number control

In website development, the content of CSS files is often changed. If you do not modify the cache settings, the browser will re-download the file after the cache expires, causing the website to load slower.

To solve this problem, we can add the version number to the URL of the CSS file, for example style.css?v=1.0. Every time the file content changes, you only need to update the version number, and the browser will think it is a new file and download it again.

2. Split CSS files

Sometimes the CSS files we write may be very large, causing the page rendering speed to slow down. At this point, we can split the CSS file into several smaller files so that the browser can download them in parallel.

At the same time, inlining commonly used CSS parts into HTML can avoid loading multiple small files and improve page loading speed.

3. Enable Gzip compression

Gzip compression is a server-side way of compressing text files (such as CSS files). It can significantly reduce file size, thereby speeding up file downloads.

In web servers such as Nginx or Apache, we can enable Gzip compression through configuration.

4. Use CDN

CDN is a centralized, distributed deployment service that can cache resource files on multiple servers around the world, thereby improving file loading speed.

When we host CSS files on a CDN, when users visit the website, the files will be loaded through the nearest CDN server, thus speeding up page rendering.

Mainstream CDN service providers include Alibaba Cloud, Tencent Cloud, Huawei Cloud, etc.

4. Summary

CSS cache setting is an important part of website optimization. By setting the cache appropriately, you can significantly reduce file download time and improve website performance and user experience. In actual development, we need to choose a cache setting solution that suits us based on specific circumstances, and continuously optimize to improve website performance.

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