Revealing the secret of HTML caching mechanism: essential knowledge points

HTML caching mechanism revealed: essential knowledge points, specific code examples required

In web development, performance has always been an important consideration. The HTML caching mechanism is one of the keys to improving the performance of web pages. This article will reveal the principles and practical skills of the HTML caching mechanism, and provide specific code examples.

1. Principle of HTML caching mechanism

During the process of accessing a Web page, the browser requests the server to obtain the HTML page through the HTTP protocol. The HTML caching mechanism is to cache HTML pages on the browser side to reduce the number of requests to the server.

Specifically, when the browser requests the page for the first time, the server will return a response header with a cache identifier (such as Etag or Last-Modified). The browser stores this response header information and caches the HTML page in the local cache. The next time the same page is requested, the browser sends the stored cache identification information to the server. The server determines whether a new page needs to be returned based on the cache identification information. If the server determines that there is no need to return a new page, it returns a 304 status code to tell the browser to continue using the cached page.

2. Practical skills

1. Set the cache expiration time

Setting the cache expiration time of the HTML page on the Web server can effectively control the browser's The cache time of this page. In general, static HTML pages can be cached for a longer period of time, such as a week or a month. Dynamic HTML pages can be set for a shorter cache time, such as one hour or one day. By properly setting the cache expiration time, you can improve the performance of page access while ensuring that the page is updated.

2. Forced refresh mechanism

When the page is updated, sometimes it is necessary to force the browser to refresh the cache to obtain the latest page content. Forced refresh can be achieved by adding parameters to the URL. For example, add a timestamp parameter after the URL, and set the value of the parameter to the current timestamp every time the page is updated. In this way, the browser will think that the URL requested each time is different, and will ignore the cache and obtain the latest page content directly from the server.

3. Version number control mechanism

In some cases, the static resources (such as CSS and JS files) in the page change, but the HTML page does not change. In order to make the browser reload static resources, you can add a version number parameter to the URL. Every time the static resource changes, the value of the version number parameter is updated. In this way, the browser will think that the URL requested is different each time and reload the static resource.

3. Specific code examples

1. Set the cache expiration time

Add the Content-Type and Cache-Control fields in the response header of the web server , set the cache expiration time.

HTTP/1.1 200 OK Content-Type: text/html; charset=utf-8 Cache-Control: max-age=604800

Among them, max-age=604800 indicates that the cache expiration time is one week.

2. Forced refresh mechanism

Add a timestamp parameter after the URL and set its value to the current timestamp.

http://example.com/page.html?_t=1596046321438

Change the timestamp value every time the page is updated.

3. Version number control mechanism

Add a version number parameter to the URL and set its value to the version number of the static resource.

http://example.com/style.css?v=2.0

Every time the static resource changes, update the value of the version number.

4. Summary

HTML caching mechanism is one of the important means to improve the performance of Web pages. By properly setting the cache expiration time, forced refresh mechanism, and version number control mechanism, you can make better use of the browser's caching mechanism and improve page access performance. The code examples provided above can help developers better understand and apply the HTML caching mechanism.

(Note: This article mainly introduces the basic principles and practical skills of the HTML caching mechanism, and provides specific code examples for readers to refer to and learn from. In specific practice, reasonable adjustments should be made based on project needs and actual conditions. Configure and adjust.)

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