Understand the version evolution and updates of Ajax

In recent years, Ajax has attracted much attention as a front-end development technology, and its application scenarios are becoming more and more widespread. In Web pages, Ajax allows users to communicate asynchronously with the server without refreshing the page and update page data in real time. With the continuous progress and evolution of technology, Ajax is also constantly updated and upgraded, from the original XMLHttpRequest to the current various front-end frameworks and libraries, making front-end development more convenient and greatly improving the user experience.

Historical changes

The name Ajax comes from Asynchronous JavaScript and XML (asynchronous JavaScript and XML), which was first released in 2005. Before the advent of Ajax, the page needed to submit a form to obtain data and refresh the page, which greatly reduced the user experience. With the emergence of Ajax, the page can obtain data through asynchronous communication and update the page content without refreshing the page, realizing a new interaction method.

During the development of Ajax, XMLHttpRequest has always been the core technology of Ajax communication. XMLHttpRequest was first introduced by Microsoft in the IE browser. It is an HTTP-based request method that can obtain data from the server asynchronously and update the page content without refreshing the page. This makes interactions more efficient, smooth and fast.

Later, with the emergence of various JavaScript libraries and frameworks, front-end development became more convenient and faster. For example, frameworks such as jQuery, AngularJS and React further improve the efficiency and reliability of front-end development based on Ajax.

Update and evolution

In the development process of Ajax, XMLHttpRequest is also constantly upgraded, and new features are introduced to adapt to different application scenarios. The following is a detailed introduction to the version update and evolution process of Ajax.

XMLHttpRequest Level 1

XMLHttpRequest Level 1 is the earliest version, supporting asynchronous HTTP requests and basic request and response headers. Through the open() and send() methods, you can send HTTP requests to the server and receive responses.

XMLHttpRequest Level 2

XMLHttpRequest Level 2 introduces new features on the basis of Level 1, such as the basic functions of uploading and downloading files on the client side, supporting cross-domain requests, etc. . At the same time, Level 2 also provides a simpler API, making the code easier to read and write.

XMLHttpRequest Level 3

XMLHttpRequest Level 3 is an upgraded version of Level 2, providing a more powerful and flexible API. For example, Level 3 can set different values ​​for different request headers when requesting, and implement progress monitoring when uploading files. At the same time, this version also adds new types of request response entities such as Blob and ArrayBuffer.

jQuery

jQuery is a very popular and practical JavaScript library. It simplifies many repetitive tasks in the JavaScript development process and provides a powerful support library. In jQuery, the Ajax function can be easily implemented using the $.ajax() function and supports multiple data types and data formats.

AngularJS

AngularJS is a front-end framework developed by Google. It provides very convenient data binding, template system and componentized architecture. In AngularJS, HTTP requests and responses can be easily implemented through the $http service, and more powerful functions can be achieved with instructions and filters. AngularJS also provides some combined services, such as $httpBackend, which can be used to simulate Ajax responses to achieve rapid front-end and back-end development and testing.

React

React is a front-end framework developed by Facebook, which adopts component-based design ideas and virtual DOM technology. In React, you can use Axios, FetchAPI and XMLHttpRequest to implement Ajax functions.

Example Demonstration

Next, we use some specific code examples to show the process of Ajax version update and evolution.

XMLHttpRequest Level 1

function httpRequest(method, url, callback, data) {
  // 创建XMLHttpRequest对象
  var xhr = new XMLHttpRequest();
  // 打开请求
  xhr.open(method, url, true);
  
  xhr.onreadystatechange = function() {
    // 判断是否完成
    if (xhr.readyState === XMLHttpRequest.DONE) {
      // 判断请求是否成功
      if (xhr.status === 200) {
        callback(xhr.responseText);
      } else {
        console.error('Ajax请求失败');
      }
    }
  };
  
  // 发送请求
  xhr.send(data || null);
}

httpRequest('POST', '/api/test', function(res) {
  console.log(res);
}, 'data=test');

XMLHttpRequest Level 2

function httpRequest(method, url, callback, data) {
  // 创建XMLHttpRequest对象
  var xhr = new XMLHttpRequest();
  // 打开请求
  xhr.open(method, url, true);
  
  xhr.onreadystatechange = function() {
    // 判断是否完成
    if (xhr.readyState === XMLHttpRequest.DONE) {
      // 判断请求是否成功
      if (xhr.status === 200) {
        callback(xhr.response);
      } else {
        console.error('Ajax请求失败');
      }
    }
  };
  
  // 发送请求
  xhr.send(data || null);
}

httpRequest('GET', '/api/test', function(res) {
  console.log(res);
}, null);

jQuery

$.ajax({
  url: "/api/test",
  type: "POST",
  data: { data: "test" },
  dataType: "json",
  success: function(res) {
    console.log(res);
  },
  error: function(err) {
    console.error('Ajax请求失败');
  }
});

AngularJS

$http({
  method: "POST",
  url: "/api/test",
  data: { data: "test" }
}).then(function(res) {
  console.log(res.data);
}, function(err) {
  console.error('Ajax请求失败');
});

React

import axios from 'axios';

axios.post('/api/test', { data: 'test' })
  .then(function(res) {
    console.log(res.data);
  })
  .catch(function(err) {
    console.error('Ajax请求失败');
  });

Conclusion

Through the introduction and demonstration of this article, we can see the continuous updating and evolution of Ajax technology. From XMLHttpRequest Level1 to frameworks such as jQuery, AngularJS and React, front-end development has become more convenient and efficient. I believe that with the continuous advancement of technology, Ajax will continue to become an indispensable part of front-end development in the future development process.

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