Revealing the essential attributes of AJAX: optimizing web page interaction experience

AJAX (Asynchronous JavaScript and XML) technology is a technology used to realize asynchronous data interaction between web pages and servers. It can improve the interactive experience of web pages and realize part of the page content. Refresh without reloading the entire page. As a front-end developer, it is very important to understand the necessary attributes of AJAX.

1. XMLHttpRequest object
In AJAX, the XMLHttpRequest object is the core of communication with the server. Through this object, you can send HTTP requests to the server and obtain the data returned by the server. Its common attributes and methods are as follows:

1. readyState: used to indicate the current status of the request, with values ​​from 0 to 4, indicating that the request has not been initialized, has been started, is sending data, and is receiving data. and the data transfer is completed.
2. open(method, url, async): used to initialize a new request for sending a request to the server. The parameter method indicates the type of request, such as GET, POST, etc.; url indicates the address of the request; async indicates Whether the request is asynchronous, the default is true, which means asynchronous.
3. send(data): Used to send the request to the server. The parameter data represents the data sent, which can be a string or a FormData object.
4. setRequestHeader(header, value): Used to set the value of the HTTP request header. Commonly used ones include Content-Type, Accept, etc.
5. onreadystatechange: used to specify a callback function, which will be triggered when the readyState attribute changes.

The following is an example of using the XMLHttpRequest object to send a GET request:

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

2. responseText and responseXML
After communicating with the server, the data returned by the server can be passed through the XMLHttpRequest object Get the responseText or responseXML attribute.

responseText is the text data returned by the server. You can obtain a text string returned by the server through this attribute. responseXML parses the text data returned by the server into an XML document object. The XML data returned by the server can be obtained through this attribute.

The following is an example of using responseText to obtain data:

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

3. onload and onerror events
In the process of processing AJAX requests, you can use onload and onerror events to handle request success and In case of request error.

The onload event is triggered when the request is successful, where the returned data can be processed. The onerror event is triggered when an error occurs in the request, and the error situation can be handled in it.

The following is an example of using onload and onerror events to process request results:

const xhr = new XMLHttpRequest();
xhr.onload = function() {
  if (xhr.status === 200) {
    const data = JSON.parse(xhr.responseText);
    console.log(data);
  }
};
xhr.onerror = function() {
  console.log("请求发生错误");
};
xhr.open("GET", "https://api.example.com/data", true);
xhr.send();

To sum up, the necessary attributes of AJAX are what developers must understand when using AJAX for asynchronous data interaction. and mastered. Through the properties and methods of the XMLHttpRequest object, you can send a request to the server and process the returned data, and use the responseText and responseXML properties to obtain the data returned by the server. Use the onload and onerror events to handle the success and error conditions of the request. Understanding and skillfully using these properties and methods can effectively improve the interactive experience of web pages.

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