Question

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How do I add a delay in a JavaScript loop?

I want to send some POST request from xmlhttp object using javascript without waiting for the response after some sleep. Inside a for loop, this request is being sent. If i am sending all the request without waiting, my browser becomes not responding for a while also it is not allowed from the server side. How can i put sleep among all these POST request?
This is what i am using-

for (var i = 0; i < users.length; i++) {
    var http = new XMLHttpRequest();
    //set args here, which is based elements of array users
    http.open('POST', '/user/home/index.php', true);
    //Set all headers here then send the request
    http.send(args);
}

Answer 1

There’s no way to delay current script execution. You’ll have to use async request and restructure your code.

So if you have your code like this:

function postData() {
    for (var i = 0; i < users.length; i++) {
        var http = new XMLHttpRequest();
        //set args here, which is based elements of array users
        http.open('POST', '/user/home/index.php', true);
        //Set all headers here then send the request
        http.send(args);
        //access request result
        if (http.status == 200) {
            console.log(http.responseText);
        } else {
            console.log('request error');
        }
    }
}

Change it like this:

var userIndex = 0;

function postData() {
    if (userIndex >= users.length) {
        //no more users to process
        return;
    }

    var http = new XMLHttpRequest();
    //set args here, which is based elements of array users
    http.open('POST', '/user/home/index.php', true);

    //set request handler
    http.onreadystatechange = function() {
        if (http.readyState != 4) return;
        if (http.status == 200) {
            console.log(http.responseText);
        } else {
            console.log('request error');
        }
        //process next user index
        userIndex++;
        window.setTimeout(function() {
            postData(); //do it again
        }, 5000); //5 seconds delay
    };

    //Set all headers here then send the request
    http.send(args);
}

postData(); //start the request chain