A closer look at AJAX: revealing the full picture of its properties-JS Tutorial-php.cn

A closer look at AJAX: revealing the full picture of its properties

王林

Release： 2024-01-30 10:11:17

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A closer look at AJAX: revealing the full picture of its properties

In-depth understanding of AJAX: To explore the full scope of its properties, specific code examples are required

Introduction:
In the field of web development, AJAX (Asynchronous JavaScript and XML) is A commonly used technology, it realizes the function of asynchronously updating the page by exchanging data with the server in the background without refreshing the entire page. This article will deeply explore the properties of AJAX, including understanding its working principle, commonly used properties and methods, and providing specific code examples to help readers better understand the application of AJAX.

1. The working principle of AJAX
The working principle of AJAX can be summarized in the following steps:

Create an XMLHttpRequest object: Use JavaScript to create an XMLHttpRequest object, which is responsible for Communicate with the server.
Establish a connection with the server: Use the open method of the XMLHttpRequest object to specify the server address and communication method (GET or POST) to be connected.
Send a request: Use the send method of the XMLHttpRequest object to send the request to the server.
Receive the server's response: Monitor the server's response status through the onreadystatechange method of the XMLHttpRequest object. Once the server's response status changes, the corresponding event processing function will be triggered.
Processing server response: In the event processing function, use the responseText or responseXML attribute of the XMLHttpRequest object to obtain the data returned by the server.
Update page content: Use JavaScript to update the corresponding part of the page based on the obtained data.

2. Commonly used AJAX attributes and methods

Attributes:
readyState: Indicates the status of the XMLHttpRequest object, 0 means not initialized, 1 means in progress Loading, 2 means loaded, 3 means interactive, 4 means completed.
status: Indicates the HTTP status code of the server response. Common ones include 200 indicating success, 404 indicating resource not found, 500 indicating internal server error, etc.
responseText: Returns the server's response data in string form.
responseXML: Returns the server's response data in the form of an XML object.
Method:
open(method, url, async): Initialize a request. The parameter method indicates the communication method. Commonly used ones are GET and POST; url indicates the server address; async indicates whether it is asynchronous. Default is true.
send(data): Send a request to the server. The parameter data represents the data that needs to be passed to the server.
setRequestHeader(header, value): Set the attributes and values of the HTTP request header, usually used to set properties such as Content-Type and Authorization.
abort(): Cancel the currently executing request.

3. Specific code examples
The following is a sample code that uses AJAX to obtain server data and update page content:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>AJAX示例</title>
</head>
<body>
  <button onclick="loadData()">加载数据</button>
  <div id="result"></div>
  <script>
    function loadData() {
      var xhr = new XMLHttpRequest();
      xhr.onreadystatechange = function() {
        if (xhr.readyState === 4 && xhr.status === 200) {
          var response = JSON.parse(xhr.responseText);
          document.getElementById("result").innerHTML = "数据：" + response.data;
        }
      };
      xhr.open("GET", "http://example.com/api/data", true);
      xhr.send();
    }
  </script>
</body>
</html>

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In the above example, call by clicking the button The loadData function creates an XMLHttpRequest object xhr and sets its onreadystatechange event handling function. Then the GET method is specified to request the server data through the open method, and finally the request is sent and the response data is obtained. In the event handling function, parse the server response data into a JSON object, and update the content of the div element with the id "result" in the page.

Conclusion:
Through the introduction of this article, we have an in-depth understanding of the working principle of AJAX, commonly used properties and methods, and provide a specific code example. The characteristics of AJAX make web development more efficient and flexible, and can obtain data and update pages asynchronously to improve user experience. I hope that readers can better understand and use AJAX technology through studying this article.

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