Discuss common methods and writing methods of using Ajax in JavaScript

JavaScript combined with Ajax is one of the keys to building modern web applications. Ajax (Asynchronous JavaScript and XML) is a technology for sending and receiving data to the server without reloading the entire page. In the following article, we will explore the common methods and writing methods of using Ajax in JavaScript.

The Four Steps of Ajax

Before you dive into how to use Ajax in JavaScript, you need to understand the four steps of Ajax:

1. Create an XMLHttpRequest object

First, you need to create an XMLHttpRequest object using JavaScript. This will allow you to request data from the server asynchronously.

2. Send a request

Once the XMLHttpRequest object is created, you need to use it to send HTTP requests. The type of request depends on your needs. Typically, GET requests are used to get data from the server, while POST requests are used to send data to the server.

3. Processing the response

The server will return the response through the XMLHttpRequest object. The results can be in plain text, XML document or JSON format.

4.Update Page

Once you receive the response from the server, you can use JavaScript to update your web page. You can update the page through HTML DOM operations, such as adding, deleting, changing elements, etc.

The following are some common Ajax writing methods:

Using the XMLHttpRequest object

The most common method is to use the XMLHttpRequest object to send and receive data. Below is a basic example of sending a request to the server and updating the page when a response is received.

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
        if (xhr.status === 200) {
            document.getElementById("result").innerHTML = xhr.responseText;
        } else {
            alert('Error: ' + xhr.status);
        }
    }
};
xhr.open('GET', 'example.php', true);
xhr.send(null);

In this example, we create an XMLHttpRequest object and set the onreadystatechange function. This function will be called when the response is received. In this function, we check the readyState attribute and status attribute to determine whether the response was successful. If successful, we use the DOM API to update the page.

Using jQuery Library

jQuery is a very popular JavaScript library that simplifies the use of Ajax. Below is an example of using jQuery to make a request on the server and update the page.

$.ajax({
    url: 'example.php',
    method: 'GET',
    success: function(result) {
        $('#result').html(result);
    },
    error: function(xhr, status, error) {
        console.log('Error: ' + error);
    }
});

In this example, we use the $.ajax() function to make a request to the server. We set the url attribute to specify the URL of the request, the method attribute to specify the type of request, the success function to handle a successful response, and the error function to handle an error response.

Using the Fetch API

The Fetch API is a new JavaScript API for making network requests to the server. Unlike the XMLHttpRequest object, it is based on Promise and provides a more streamlined way to send and receive network requests. Below is an example of using the Fetch API to send a request and update a page.

fetch('example.php')
    .then(response => response.text())
    .then(result => {
        document.getElementById("result").innerHTML = result;
    })
    .catch(error => {
        console.log('Error: ' + error);
    });

In this example, we use the fetch() function to send a request to the server. We use the then() function to handle successful responses and the catch() function to handle error responses. After successfully processing the response, we update the page using the DOM API.

Summary

In modern web applications, JavaScript and Ajax are essential. Using JavaScript's XMLHttpRequest object, the jQuery library, or the Fetch API, you can easily make requests to the server and receive responses, and update the page using the DOM API. Whichever method you choose, remember to use a try-catch block to catch any potential exceptions.

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