Callback called when a task finish OR already finished

Question

I have a simple code that involves asynchronous tasks:

// The NewsFeed Class

function NewsFeed() {

    this.loadFeed = function() {
        $.ajax({
            url: "http://www.example.com",
            success: function() {
                // doSomething here, and call onload.
            }
        });
    }

    // Need to implement onload here somehow
    this.onload = ?;

    this.loadFeed();
    return this;

}
NewsFeed.constructor = NewsFeed;



// In main JS file
var newsFeed = new NewsFeed();
$(function() {
    // do something
    newsFeed.onload = function() { // do something when news feed is loaded };
}

My requirement is that, onload of NewsFeed needed to be executed in both case:

• If the loadFeed's ajax is finished, run it immediately.
• If the loadFeed's ajax is not done yet, run after it.

Answer 1

There's really no need to use new or constructor when you don't need new instances, all you really need is to run a simple ajax function that gets the result from cache if it hasn't changed.

function newsFeed() {
   return $.ajax({
       url   : "http://www.example.com",
       cache : true // let the browser handle caching for you
   });
}


// In main JS file
$(function() {
    newsFeed().then(function() { 
        // do something when news feed is loaded 
    });
});

Answer 2

The new pattern instead of callback is using Promises see: https://github.com/kriskowal/q

With jquery you can use: https://api.jquery.com/category/deferred-object/

now the code:

 function NewsFeed() { function loadFeed() { var deferred = $.Deferred(); $.ajax({ url: "http://www.example.com", success: function(data) { deferred.resolve(data); }, error: function(data) { deferred.reject(data); } }); return deferred.promise(); } this.loadFeed = loadFeed; return this; } NewsFeed.constructor = NewsFeed; // In main JS file var newsFeed = new NewsFeed(); newsFeed.loadFeed().done(function(data){ //data loaded successfully }) .fail(function(data){ //ajax request failed }) .always(function(){ //finally: });