jQuery Ajax / .each callback, next 'each' firing before ajax completed

Question

Hi the below Javascript is called when I submit a form. It first splits a bunch of url's from a text area, it then:

1) Adds lines to a table for each url, and in the last column (the 'status' column) it says "Not Started".
2) Again it loops through each url, first off it makes an ajax call to check on the status (status.php) which will return a percentage from 0 - 100.
3) In the same loop it kicks off the actual process via ajax (process.php), when the process has completed (bearing in the mind the continuous status updates), it will then say "Completed" in the status column and exit the auto_refresh.
4) It should then go to the next 'each' and do the same for the next url.

function formSubmit(){

    var lines = $('#urls').val().split('\n');

    $.each(lines, function(key, value) {
        $('#dlTable tr:last').after('<tr><td>'+value+'</td><td>Not Started</td></tr>');
    });

    $.each(lines, function(key, value) {

        var auto_refresh = setInterval( function () {
            $.ajax({
              url: 'status.php',
              success: function(data) {
            $('#dlTable').find("tr").eq(key+1).children().last().replaceWith("<td>"+data+"</td>");
              }
            });
        }, 1000);

        $.ajax({
          url: 'process.php?id='+value,
          success: function(msg) {
        clearInterval(auto_refresh);
        $('#dlTable').find("tr").eq(key+1).children().last().replaceWith("<td>completed rip</td>");
          }
        });

    });

}

Answer 1

What you want is to run several asynchronous actions in sequence, right? I'd build an array of the functions to execute and run it through a sequence helper.

https://github.com/michiel/asynchelper-js/blob/master/lib/sequencer.js

var actions = [];
$.each(lines, function(key, value) {

    actions.push(function(callback) {
      $.ajax({
          url: 'process.php?id='+val,
          success: function(msg) {
            clearInterval(auto_refresh);

            //
            // Perform your DOM operations here and be sure to call the
            // callback!
            //

            callback();
          }
        });
    });
  }
);

As you can see, we build an array of scoped functions that take an arbitrary callback as an argument. A sequencer will run them in order for you.

Use the sequence helper from the github link and run,

var sequencer = new Sequencer(actions);
sequencer.start();

It is, btw, possible to define sequencer functions in a few lines of code. For example,

function sequencer(arr) {
    (function() {
        ((arr.length != 0) && (arr.shift()(arguments.callee)));
    })();
}

Answer 2

AJAX is asynchronous.

That's exactly what's supposed to happen.

Instead of using each, you should send the next AJAX request in the completion handler of the previous one.