jquery ajax duplicate request

When using jquery ajax to request data, we often encounter a problem, that is, sending multiple repeated requests. This situation may cause increased server stress or even crash. To avoid this, we need to understand the reasons for duplicate requests and find solutions.

1. The asynchronous request mechanism of jQuery ajax

Before understanding the reasons for repeated requests, let’s take a look at the working mechanism of jQuery ajax.

Normally, we use jQuery's $.ajax() method to send asynchronous requests. This method receives an object as a parameter, including various settings of the request, such as the requested URL, request method, data type, etc. The specific usage is as follows:

$.ajax({
    url: 'http://www.example.com/data',
    type: 'GET',
    dataType: 'json',
    success: function(response){
        // 获得数据成功后的处理
    }
});

This request will send a GET request to the URL http://www.example.com/data, expecting to get a response in JSON format. If the request is successful, the success callback function will be executed and the response data will be passed in as a parameter.

This is a typical asynchronous request, which does not block the page, but occurs in the background. When the request is sent, jQuery will continue to execute the following code and wait for the server to respond. Once the response is received, the success callback function is triggered and the corresponding processing code is executed.

2. Cause of duplicate requests

In some cases, we may find that the browser sends multiple duplicate requests. For example, if the user clicks a button multiple times in a short period of time, an ajax request will be sent for each click. This may cause a significant increase in server load or even crash.

There are many reasons for repeated requests, among which the more common ones are as follows:

(1) Code errors

When we write code, errors may occur , such as accidentally writing an ajax request in a loop. This will result in multiple repeated requests. Therefore, you must pay attention to the correctness of the logic when writing code.

(2) Network delay

Due to the instability of the network, sometimes requests may be delayed. If we click the button multiple times while waiting for a response, multiple duplicate requests will be sent.

(3) The server responds slowly

When the server responds slowly, we may feel impatient and click the button again to send a new request. This will also lead to duplicate requests.

3. Methods to solve repeated requests

In order to avoid repeated requests, we can use the following methods:

(1) Disable button

When the user clicks the button, we can disable the button for a period of time and then enable it after the request is completed. This prevents users from clicking the button repeatedly and sending multiple identical requests.

The specific implementation method is as follows:

$('#myButton').on('click', function(){
    $(this).prop('disabled', true);
    $.ajax({
        url: 'http://www.example.com/data',
        type: 'GET',
        dataType: 'json',
        success: function(response){
            $('#myButton').prop('disabled', false);
            // 处理响应数据
        }
    });
});

Here, when we click the button, we set the disabled attribute of the button to true to disable the button. After the request is completed, set the disabled attribute of the button to false to enable the button.

(2) Limit the frequency of requests

We can determine the time of the last request when sending a request. New requests are only allowed to be sent if no request is sent within a certain time interval. This way you can limit the frequency of requests and avoid excessive request pressure.

The specific implementation method is as follows:

var lastRequestTime = 0; // 上一次请求的时间

$('#myButton').on('click', function(){
    var now = new Date().getTime(); // 当前时间
    if(now - lastRequestTime > 1000){ // 限制请求频率为1秒
        $.ajax({
            url: 'http://www.example.com/data',
            type: 'GET',
            dataType: 'json',
            success: function(response){
                // 处理响应数据
            }
        });
        lastRequestTime = now;
    }
});

Here, we record the time of the last request. Each time the button is clicked, we determine whether the current time is more than 1 second from the time of the last request. If it exceeds, new requests are allowed to be sent.

(3) Cancel the previous request

If the previous request has not been completed, we can cancel it to avoid sending multiple repeated requests.

The specific implementation method is as follows:

var xhr = null; // 存储ajax请求的xhr对象

$('#myButton').on('click', function(){
    if(xhr){ // 如果前一次请求还没有完成，取消它
        xhr.abort();
    }
    xhr = $.ajax({
        url: 'http://www.example.com/data',
        type: 'GET',
        dataType: 'json',
        success: function(response){
            // 处理响应数据
        }
    });
});

Here, we define a global xhr variable to store the xhr object of the last ajax request. Before each new request is sent, first determine whether xhr exists. If it exists, call the abort() method to cancel the previous request. Then, send a new request.

4. Summary

Duplicate requests are a common problem that can stress the server or even crash it. In order to avoid this situation, we can use methods such as disabling buttons, limiting request frequency, and canceling the previous request. When writing code, be sure to pay attention to the correctness of the logic to avoid repeated requests.

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