A Deep Dive into How AJAX Requests Work: Revealing the Different AJAX Request Methods

In-depth understanding of AJAX: Explore different methods of AJAX requests, specific code examples are required

Introduction:
As web applications evolve, user-friendly User interface is getting more and more attention. AJAX (Asynchronous JavaScript and XML) technology emerged as the times require. It can communicate asynchronously with the server to achieve partial updates without refreshing the entire page. This article will provide an in-depth look at the different request methods of AJAX and provide specific code examples.

1. AJAX request method:
There are many AJAX request methods, and you can choose the appropriate method according to different needs.

1. GET request:
   The GET request is one of the most common AJAX request methods and is usually used to obtain data on the server. The GET request passes parameters through the URL and requires the server to return the corresponding data to the browser as part of the URL. The following is a sample code for a GET request:

var request = new XMLHttpRequest();
request.open('GET', 'data.php?id=123', true);
request.onreadystatechange = function() {
  if (request.readyState === 4 && request.status === 200) {
    var response = request.responseText;
    // 处理返回的数据
  }
}
request.send();

2. POST request:
   POST request is often used to submit data to the server. Compared with GET requests, POST requests put parameters in the request body in JSON format instead of in the URL. The following is a sample code for a POST request:

var request = new XMLHttpRequest();
request.open('POST', 'submit.php', true);
request.setRequestHeader('Content-Type', 'application/json');
request.onreadystatechange = function() {
  if (request.readyState === 4 && request.status === 200) {
    var response = request.responseText;
    // 处理返回的数据
  }
}
var data = { username: 'john', password: '123456' };
request.send(JSON.stringify(data));

3. PUT request:
   PUT request is used to update resources to the server. The difference between a PUT request and a POST request is that the PUT request is idempotent, that is, executing the same PUT request multiple times will produce the same result. The following is a sample code for a PUT request:

var request = new XMLHttpRequest();
request.open('PUT', 'update.php', true);
request.setRequestHeader('Content-Type', 'application/json');
request.onreadystatechange = function() {
  if (request.readyState === 4 && request.status === 200) {
    var response = request.responseText;
    // 处理返回的数据
  }
}
var data = { id: 123, name: 'John' };
request.send(JSON.stringify(data));

4. DELETE request:
   DELETE request is used to delete resources from the server. DELETE requests are also idempotent, and executing the same DELETE request multiple times will produce the same result. The following is a sample code for a DELETE request:

var request = new XMLHttpRequest();
request.open('DELETE', 'delete.php?id=123', true);
request.onreadystatechange = function() {
  if (request.readyState === 4 && request.status === 200) {
    var response = request.responseText;
    // 处理返回的数据
  }
}
request.send();

2. Common problems and solutions to AJAX:
In the process of using AJAX, you may encounter some common problems, listed below Some common problems and solutions.

1. Cross-domain request problem:
   Due to the browser's same-origin policy restrictions, AJAX requests can only make requests to resources under the same domain name by default. If you need cross-domain requests, you can use JSONP, CORS and other technologies to solve cross-domain problems.
2. Request timeout problem:
   If the response time of the AJAX request is too long, it may cause the request to timeout. In order to avoid this problem, you can set an appropriate timeout and handle the corresponding logic when the timeout occurs.

var request = new XMLHttpRequest();
request.open('GET', 'data.php', true);
request.timeout = 5000;
request.ontimeout = function() {
  // 处理超时逻辑
}
request.send();

3. Security issues:
   In AJAX requests, attention needs to be paid to protecting the user's security information. Security measures such as the HTTPS protocol can be used to ensure the security of data transmission.

Conclusion:
This article provides an in-depth understanding of the different request methods of AJAX and provides specific code examples. Different request methods can meet different needs, and we can choose the appropriate request method according to the actual situation. At the same time, it also introduces some common problems and solutions, hoping to help everyone understand AJAX in depth. Through the flexible use of AJAX, we can improve the user experience of web applications and present users with a more friendly interface.

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