Master performance optimization and code compression in JavaScript

Mastering performance optimization and code compression in JavaScript requires specific code examples

As the complexity of web applications continues to increase, optimizing JavaScript code to improve performance changes becomes more and more important. At the same time, code compression can reduce file size and speed up loading. This article will introduce some common performance optimization techniques and code compression methods, and provide specific code examples.

1. Performance optimization tips

1. Reduce HTTP requests
   HTTP requests are a major bottleneck in the loading speed of web applications. By merging and compressing files, the number of HTTP requests can be reduced. For example, when there are multiple JavaScript files, you can use tools to merge them into one file to reduce the number of HTTP requests for the page.

   //将多个文件合并为一个文件
   //<script src="file1.js"></script>
   //<script src="file2.js"></script>
   //<script src="file3.js"></script>
   
   //合并后
   //<script src="combined.js"></script>

2. Reasonable use of cache
   Cache is an important means to improve the performance of web applications. Reasonable use of cache can avoid repeated requests and reduce network transmission time. In JavaScript, files that do not change frequently can be set to be permanently cached, such as images, CSS, and JavaScript libraries.

   //设置缓存过期时间为1年
   //<link rel="stylesheet" href="style.css" type="text/css" media="all" />
   //Expires: Thu, 31 Dec 2022 23:59:59 GMT
   
   //对于经常变化的文件，可以设置较短的缓存时间
   //<script src="main.js" type="text/javascript"></script>
   //Cache-Control: max-age=3600

3. Using event delegation
   In JavaScript, event delegation is a common technique for optimizing performance. By binding events to container elements instead of each child element, you can reduce the number of event handling functions and improve performance.

   //原始代码
   //<ul id="list">
   //  <li>Item1</li>
   //  <li>Item2</li>
   //  <li>Item3</li>
   //</ul>
   
   // for (var i = 0; i < listItems.length; i++) {
   //   listItems[i].addEventListener('click', function() {
   //     console.log('Clicked item ' + i);
   //   });
   // }
   
   //优化后的代码
   //<ul id="list">
   //  <li>Item1</li>
   //  <li>Item2</li>
   //  <li>Item3</li>
   //</ul>
   
   // list.addEventListener('click', function(event) {
   //   if (event.target.tagName === 'LI') {
   //     console.log('Clicked item ' + event.target.textContent);
   //   }
   // });

4. Avoid using global variables
   Global variables are slower to access in JavaScript. When variables are defined in the local scope, dependence on global variables can be reduced and code execution efficiency can be improved.

   //全局变量
   var x = 5;
   function foo() {
     console.log(x);
   }
   
   //局部变量
   function bar() {
     var x = 5;
     console.log(x);
   }

2. Code Compression

Code compression is a common method to reduce the size of JavaScript files. Compressed code not only speeds up loading, but also reduces network transfer time. The following are some commonly used code compression methods:

1. Remove spaces and newlines
   Spaces and newlines do not affect the execution of the code in JavaScript. They can be deleted through tools to reduce the size of the file. size.
2. Delete comments
   During the compression process, useless comments can be deleted to reduce the file size.
3. Compress variable and function names
   When variable and function names are executed in JavaScript, it is not necessary to retain the original names. You can reduce the file size by compressing them into short strings.

The above are some commonly used performance optimization techniques and code compression methods. I hope they will be helpful to you. By rationally using these technologies, you can improve the execution efficiency of JavaScript code, reduce file size, and speed up page loading.

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