Learn AJAX attributes and create efficient and practical front-end technology

Mastering AJAX attributes: To create efficient and practical front-end technology, specific code examples are required

Introduction:
With the rapid development of the Internet, front-end technology is also constantly changing Evolution and progress. As front-end developers, we often need to implement functions such as dynamically loading data and updating pages without refreshing in web pages. And AJAX (Asynchronous JavaScript and XML) is our weapon to achieve these functions. This article will introduce the relevant knowledge of AJAX attributes, help you better master AJAX, and provide specific code examples for reference.

1. The basic concepts and functions of AJAX
AJAX is a technology that updates part of the page without reloading the entire page. It realizes the ability to update web pages asynchronously by exchanging data with the server in the background.

The functions of AJAX mainly include the following aspects:

1. Realize page updates without refreshing: Through AJAX, we can update only what needs to be changed without refreshing the entire page. part, thereby improving user experience.
2. Dynamic loading of data: Data can be loaded asynchronously through AJAX, allowing the page to display the latest information in real time.
3. Improve web page performance: Because AJAX can load data asynchronously, it reduces the number of requests to the server, thereby improving web page performance and response speed.

2. Specific application of AJAX attributes

1. XMLHttpRequest object
   The core of AJAX is the XMLHttpRequest object, which can send HTTP requests and receive server responses. The following is a simple example code that uses the XMLHttpRequest object to send a GET request and receive a server response:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://example.com/api/data', true);
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    console.log(xhr.responseText);
  }
};
xhr.send();

2. GET request and POST request
   AJAX can send GET request and POST request, GET Requests are used to get data from the server, while POST requests are used to send data to the server. The following is a sample code that sends a POST request and receives a server response:

var xhr = new XMLHttpRequest();
xhr.open('POST', 'http://example.com/api/data', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    console.log(xhr.responseText);
  }
};
xhr.send(JSON.stringify({ username: 'john', password: '123456' }));

3. Cross-domain request
   AJAX cannot send cross-domain requests by default, but it can be solved by setting the server response header Cross-domain issues. The following is a sample code for sending a cross-domain request:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://example.com/api/data', true);
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    console.log(xhr.responseText);
  }
};
xhr.withCredentials = true; // 允许发送跨域请求需要设置此属性为true
xhr.send();

4. Asynchronous request and synchronous request
   AJAX defaults to an asynchronous request, that is, the subsequent code continues to be executed after the request is sent. But it can also be set as a synchronous request, that is, after sending the request, wait for the server to respond before continuing to execute subsequent code. The following is a sample code for sending a synchronous request:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://example.com/api/data', false); // 同步请求设置为false
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    console.log(xhr.responseText);
  }
};
xhr.send();

3. Summary
By learning the relevant knowledge of AJAX attributes, we can use AJAX more flexibly to achieve dynamic loading and no refresh of web pages. Updates and other functions. AJAX technology plays an important role in front-end development. Mastering it can greatly improve the interactivity and user experience of web pages. I hope that through the introduction of this article, readers can have a deeper understanding of AJAX attributes and flexibly apply them in actual development.

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