jQuery .always() seems to fire before $.get() request is actually complete

Question

This is likely a misunderstanding on my part of how AJAX functions, but I have a situation where a $.get callback (.always()) is being called before the GET request actually finishes. At least, that's what it looks like.

The Code

var apiRequest  = 'some/url/';

// fetch list of video embed codes
$.get( apiRequest, function( embed_codes ) {

    // added this per Explosion Pills' answer
    var jqxhrs = [];

    // for each embed code, get video details (name, duration, etc.)
    for ( var i = 0; i < embed_codes.length; i++ ) {
        var videoDetailsRequest = '/v2/assets/' + embed_codes[i];
        //..declare vars..

        // fetch video details
        var jqxhr = $.get( videoDetailsRequest, function( video ) {
            // build playlist entry for each video
            playlistItem = '<li><h3>' + video.name + '</h3><p>' + video.description + '</p></li>';

            // create object of video HTML, with key = "video name" for sorting later
            videoArray[video.name] = playlistItem;
        }, 'jsonp' )

        // added this per Explosion Pills' answer
        jqxhrs.push( jqxhr );
    }

    // updated from jqxhr.always( function() {
    $.when( jqxhrs ).always( function() {
        // create array of keys
        for ( k in videoArray ) {
            if ( videoArray.hasOwnProperty( k ) ) { keys.push( k ); }
        }

        // append alphabetized list of videos to the page...
    });
}, 'jsonp' );

What the Code Does

Essentially, the code does this: loop through a list of video embed codes. For each iteration of the for loop, fetch details about each video and push those details into a multidimensional array. Once done fetching all videos, call the .always() callback, which sorts the videos into an alphabetized playlist and appends to the page.

The Problem

The .always() callback sometimes gets called before all of the videos have been fetched. There are 9 videos in the playlist, but sometimes only 6 or 7 are returned before the callback is fired, which means my playlist is a bit short. I have tested this by alert()ing the number of keys and using the console. What I've seen is that 6-7 videos will return, then the alert() in the callback fires, then the remaining videos are returned.

MY QUESTION:

Why is this happening? I thought the .always() callback fired after the AJAX request was complete. Doesn't this mean that all of the videos should be returned before the callback is fired? I suspect it has to do with the "A" in AJAX, but I thought the purpose of the always() callback was to account for this. Anything to help me understand is greatly appreciated. Thanks!

Answer 1

The way you have set this up, the .always callback will fire as soon as the last ajax request in the loop completes. This can happen out of order with respect to the others. I can't tell if you want it to fire when all requests in the loop have completed or when the outer request has completed.

For the outer request, it's easy. Just chain a call to .always (or .done, I believe they are the same and the latter is preferred).

If you want it to complete when all the other ajax requests are completed, you can use $.when, which checks when all deferred objects are complete:

var jqxhrs = [];
   ...for loop...
   var jqxhr = $.get( videoDetailsRequest
   ...
   }, 'jsonp');
   jqxhrs.push(jqxhr);
...
$.when.apply(undefined, jqxhrs).always(function () { /* your intended callback */

---

Alternatively, you can use .pipe:

//Create initial deferred object
var jqxhr = $.Deferred();
   ...for loop...
   jqxhr = jqxhr.pipe($.get(...
jqxhr.always(function () { /* callback */