Wait for previous AJAX call in FOR loop

Question

How would I wait until the previous ajax call has finished before looping and doing the next call? At the moment the code loops all the way through and executes all the ajax requests at once!

<script>
var busy;

function check(mailpass, proxy){
    var post_data = {};
    var post_json = "";

    post_data['mailpass'] = mailpass;
    post_data['proxy'] = '108.36.248.67:17786';
    post_json = JSON.stringify(post_data);

    jQuery.ajax({
        url: '/postdata' ,
        type: "POST",
        data: {params: post_json},
        success: function(data){
            var obj = JSON.parse(data);

            if(obj.error == 0){
                //
                $("#acc-live").append(obj.msg + "<br/>");
            } else if(obj.error == 1){
                //
                $("#socks-die").append(obj.msg+ "<br/>");   
            } else if(obj.error == 2){
                //
                $("#acc-die").append(obj.msg+ "<br/>"); 
            }
        }
    }); 

}
$(document).ready(function(){
    $("#submit").click(function(){
        var lines = $("#lines").val().split('\n');


        for(var i = 0;i < lines.length;i++){
            check(lines[i], '123');
        }

    });

});
</script>

Answer 1

You could add the counter (currentIndex) and re-organize the code a little bit.

var busy;
var lines;
var currentIndex = 0;

function checkNext(){

    if( currentIndex >= lines.length ){
        console.log('all done');
        return;
    }

    var mailpass = lines[currentIndex];
    var proxy = '123';

    var post_data = {};
    var post_json = "";

    post_data['mailpass'] = mailpass;
    post_data['proxy'] = '108.36.248.67:17786';
    post_json = JSON.stringify(post_data);

    jQuery.ajax({
        url: '/postdata' ,
        type: "POST",
        data: {params: post_json},
        success: function(data){
            var obj = JSON.parse(data);

            if(obj.error == 0){
                //
                $("#acc-live").append(obj.msg + "<br/>");
            } else if(obj.error == 1){
                //
                $("#socks-die").append(obj.msg+ "<br/>");   
            } else if(obj.error == 2){
                //
                $("#acc-die").append(obj.msg+ "<br/>"); 
            }

            currentIndex++; //Increase the counter
            checkNext();
        }
    }); 

}
$(document).ready(function(){
    $("#submit").click(function(){
        lines = $("#lines").val().split('\n');          
        checkNext();
    });
});