Implement ajax nesting without jquery

AJAX technology is a very important part of modern Web development, which allows us to dynamically load content, interactive communication, and front-end and back-end data exchange. However, as technology continues to develop, more and more developers are beginning to use native JavaScript without using the jQuery library to implement AJAX requests to avoid additional dependencies. However, many beginners are not yet familiar with the method of implementing AJAX requests in native JavaScript, so this article will share tips on how to implement nested AJAX requests without using the jQuery library.

AJAX Introduction

AJAX (Asynchronous JavaScript and XML) is a technology based on asynchronous interaction between the browser and the server. It can issue HTTP requests and process responses through JavaScript, making the front-end page realize Asynchronous communication and partial refresh capabilities. The biggest advantage of AJAX is that it can make the interaction of the page very rich, and it can also improve the performance of the website.

Use native JS to implement nested AJAX requests

In traditional Web development, we often need to use AJAX technology to achieve some interactions with the server. Sometimes we need to send a second request after the first AJAX request is completed, but for implementation and efficiency considerations, we do not want to use libraries such as jQuery to implement nested AJAX requests. This article will demonstrate how Use native JavaScript to implement this functionality.

1. XMLHttpRequest Object

When writing AJAX using native JavaScript, we need to use the XMLHttpRequest object, also known as "XHR". The XMLHttpRequest object can send requests to the server and receive responses from the server. It can support multiple HTTP methods, such as GET, POST, PUT, etc.

The sample code is as follows:

var xhr = new XMLHttpRequest(); 
xhr.open('GET', 'url', true); 
xhr.onreadystatechange = function() { 
    if (xhr.readyState === 4 && xhr.status == 200) { 
        console.log(xhr.responseText); 
    }
}; 
xhr.send();

2. Promise object

Promise is an important object in ES6, which can perform specific actions when the asynchronous operation is completed. Content, realizing automated tasks of handling asynchronous operations. The basic method of using Promise is as follows:

const promise = new Promise((resolve, reject) => { 
    // 异步操作
    if (异步操作成功)
        resolve('Success');
    else
        reject('Failure');
}); 
promise.then((value) => { 
    console.log(value); 
}).catch((error) => { 
    console.error(error); 
});

3. Implement nested AJAX requests

Next, we use Promise to connect multiple AJAX requests in series to achieve nested Asynchronous request, the sample code is as follows:

function ajax(url) { 
    return new Promise(function (resolve, reject) { 
        var xhr = new XMLHttpRequest(); 
        xhr.open('GET', url, true); 
        xhr.onreadystatechange = function() { 
            if (xhr.readyState === 4 && xhr.status == 200) { 
                resolve(xhr.responseText); 
            } 
        }; 
        xhr.send(); 
    }); 
} 

ajax('url1').then(function(result1) { 
    return ajax('url2' + result1); 
}).then(function(result2) { 
    return ajax('url3' + result2); 
}).then(function(result3) { 
    console.log(result3); 
}).catch(function(error) { 
    console.error(error); 
});

In the above code, we first define an ajax function, which uses Promise to encapsulate the process of XMLHttpRequest executing asynchronous requests, and then access url1 in sequence, and the access result is used as when accessing url2 Parameters, nested access multiple URL addresses in sequence.

So far, we have successfully implemented nested AJAX requests using native JavaScript and achieved elegant asynchronous operations without relying on external libraries such as jQuery. This method has great advantages in terms of writing performance optimization and environmental restrictions, and is also an important skill point that cannot be ignored in web development.

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