How do you work with an array of jQuery Deferreds?

Question

I have an application that requires data be loaded in a certain order: the root URL, then the schemas, then finally initialize the application with the schemas and urls for

Answer 1

The workaround above (thanks!) doesn't properly address the problem of getting back the objects provided to the deferred's resolve() method because jQuery calls the done() and fail() callbacks with individual parameters, not an array. That means we have to use the arguments pseudo-array to get all the resolved/rejected objects returned by the array of deferreds, which is ugly:

$.when.apply($, promises).then(function() {
     var schemas=arguments; // The array of resolved objects as a pseudo-array
     ...
};

Since we passed in an array of deferreds, it would be nice to get back an array of results. It would also be nice to get back an actual array instead of a pseudo-array so we can use methods like Array.sort().

Here is a solution inspired by when.js's when.all() method that addresses these problems:

// Put somewhere in your scripting environment
if (jQuery.when.all===undefined) {
    jQuery.when.all = function(deferreds) {
        var deferred = new jQuery.Deferred();
        $.when.apply(jQuery, deferreds).then(
            function() {
                deferred.resolve(Array.prototype.slice.call(arguments));
            },
            function() {
                deferred.fail(Array.prototype.slice.call(arguments));
            });

        return deferred;
    }
}

Now you can simply pass in an array of deferreds/promises and get back an array of resolved/rejected objects in your callback, like so:

$.when.all(promises).then(function(schemas) {
     console.log("DONE", this, schemas); // 'schemas' is now an array
}, function(e) {
     console.log("My ajax failed");
});