Why is css not cached?

CSS (Cascading Style Sheets), as one of the most basic technologies in front-end development, is often used to beautify website pages and optimize user experience. However, website developers often encounter a problem when debugging CSS styles: CSS files are not cached.

What is CSS caching?

When visiting a website, the server will send some static resources to the browser, such as HTML, CSS, JavaScript, pictures and other files. To improve page load speed and user experience, browsers cache these files so that the same page loads faster the next time you visit it. This caching mechanism is called HTTP caching.

When a user visits a page for the first time, the browser will download all static resources and save them in the local cache. When the user visits the page again, the browser can read these files directly from the cache without re-downloading them. This improves page loading speed and reduces server load.

Why are CSS files not cached?

However, sometimes when developers modify CSS styles, they find that the browser does not update the styles in the page, but still loads the previous cached file. This is the problem with CSS files not caching.

The reason for this problem is the working principle of the HTTP caching mechanism. When the browser requests a static resource, it will bring a request header If-Modified-Since, which returns the Etag value of the resource to the server. The server will check this request header. If the browser's local cache has not expired, the server will return a 304 status code, indicating that the file can be obtained from the local cache. Therefore, even if the developer updates the CSS style, if the browser still requests the file with the old request header, the server will still return a 304 status code, causing the browser to not update the CSS style.

How to solve the problem of CSS files not being cached?

1. Clear browser cache

Developers can solve the problem of CSS files not being updated by clearing the browser cache. In the Chrome browser, you can open the clear data page by entering chrome://settings/clearBrowserData in the address bar, select clear browser cache and cookie data, and then click the "Clear Data" button.

2. Add the version number to the URL

Developers can add the version number to the URL of the CSS file to ensure that the browser can obtain the latest file. For example, ../style.css?v=1.0, after modifying the style, change the version number to other numbers or timestamps. The browser will think this is a new file and update the style. This method requires manual modification of file links and is suitable for smaller projects.

3. Set Cache-Control and Pragma

Developers can set Cache-Control and Pragma in the HTTP response header on the server side to control the time when the browser caches resources. and manner. For example, setting Cache-Control to no-cache or max-age=0 and Pragma to no-cache means that the browser will not cache the resource and each request will return the latest version of the file. This method is suitable for larger projects and high-traffic websites.

Conclusion

The problem of CSS files not being cached is a common problem in front-end development, but users can solve it by clearing the browser cache, using version numbers, and setting Cache-Control and Pragma. This problem improves website loading speed and user experience.

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