A brief introduction to the main functions of Ajax

Quickly understand the main functions of Ajax, you need specific code examples

Introduction:
In modern web applications, we often use Ajax (Asynchronous JavaScript and XML ) to implement asynchronous communication. Through Ajax, we can interact with data on the web page and dynamically update data without reloading the entire page. This article will introduce the main functions of Ajax and provide specific code examples.

1. The main functions of Ajax:

1. Asynchronous communication: The core function of Ajax is asynchronous communication. It can send HTTP requests in the background and get the response results without affecting the page. This improves user experience and avoids page reloading.
2. Dynamic update of data: Ajax can dynamically update data through asynchronous communication with the server. For example, in a chat application, new messages can be displayed instantly through Ajax without refreshing the page.
3. Form data submission: Ajax can be used to submit form data asynchronously to avoid page reloading. After the user fills out the form and clicks the submit button, Ajax will send the form data to the server for processing and return the processing results to the client.
4. Real-time search: Through Ajax, we can search for relevant content in real time when the user inputs without refreshing the page. When the user enters characters, Ajax can send a request in the background to obtain relevant search results and display them to the user.
5. Data acquisition and processing: Ajax can obtain and process data on the server. We can send requests through Ajax to obtain background data, and then process and display it on the front end.

2. Code example:
The following is a code example using Ajax for asynchronous communication:

function getData() {
  var xhr = new XMLHttpRequest();
  xhr.open("GET", "data.json", true);
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      var data = JSON.parse(xhr.responseText);
      // 在这里对数据进行处理和展示
    }
  };
  xhr.send();
}

The above code uses the XMLHttpRequest object to send GET request to obtain the data in the data.json file. When the request returns successfully, the response result is converted into a JSON object through the JSON.parse() method, and then the data can be processed and displayed.

In addition to GET requests, we can also use Ajax to send POST requests:

function postData() {
  var xhr = new XMLHttpRequest();
  xhr.open("POST", "http://example.com/api", true);
  xhr.setRequestHeader("Content-Type", "application/json");
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      var response = JSON.parse(xhr.responseText);
      // 在这里对响应数据进行处理和展示
    }
  };
  var data = {
    username: "John",
    password: "12345"
  };
  xhr.send(JSON.stringify(data));
}

The above code uses the XMLHttpRequest object to send POST requests to http://example .com/api interface, and set the Content-Type of the request header to application/json. Convert the data into a JSON string through the JSON.stringify() method and send it to the server through the send() method. When the request returns successfully, the response data can be processed and displayed.

Conclusion:
Through the above introduction and code examples, I hope readers can quickly understand the main functions of Ajax. Ajax can realize asynchronous communication, dynamic data update, form data submission, real-time search, data acquisition and processing and other functions, which greatly improves the user experience and performance of web applications. By using Ajax, we can achieve more flexible and efficient web page interaction.

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