javascript sends ajax request parameters

JavaScript is one of the most commonly used programming languages ​​on the Internet and can be used to add dynamic interactivity to websites. AJAX is a technology for asynchronous data exchange with the server without refreshing the entire page. On many websites, we can see examples of obtaining data through AJAX. How to send an AJAX request and receive a return value using JavaScript? This article will introduce it to you.

The main steps to send an AJAX request include:

1. Create an XMLHttpRequest object
2. Specify the request method and request address
3. Set the request header information
4. Send a request
5. Receive and process the data returned by the server
6. Create the XMLHttpRequest object

First create the XMLHttpRequest object through JavaScript code.

var xhr = new XMLHttpRequest();

2. Specify the request method and request address

Next, we need to specify the request method and request address. For example, if we need to use the GET method to send a request to /api/data.php, we can use the following code.

xhr.open('GET', '/api/data.php', true);

The first parameter specifies the request method, the second parameter specifies the request address, and the third parameter specifies whether to execute asynchronously, usually true.

If you need to use the POST method, you can use the following code.

xhr.open('POST', '/api/data.php', true);

3. Set request header information

Before sending the request, we also need to set the request header information. For example, you can set the Content-Type to application/x-www-form-urlencoded.

xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');

4. Send a request

Next, we can use the send() method to send a request. If you use the GET method, you can just pass in an empty string as a parameter. For example:

xhr.send('');

If you use the POST method, you can pass in the data that needs to be sent. For example:

xhr.send('name=John&age=25');

5. Receive and process data returned by the server

When the server returns a response, we can detect the request status through the readyState attribute. readyState has five possible values:

• 0 (uninitialized): Indicates that the xhr object has been created, but the open() method has not been called.
• 1 (Sending): Indicates that the open() method has been called, but the send() method has not been called.
• 2 (Sent): Indicates that the send() method has been called, but the server has not yet returned a response.
• 3 (Receiving): Indicates that the response has started to be received but has not been completed.
• 4 (Complete): Indicates that the response has been completed and the data returned by the server can be accessed.

We can use the following code to listen for changes in readyState.

xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        // 处理服务器返回的数据
        console.log(xhr.responseText);
    }
}

When readyState reaches 4, we can access the responseText property to get the response information returned by the server.

The above are the basic steps for sending AJAX requests using JavaScript. With these steps, we can easily send an asynchronous request to the server and get the response data.

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