jQuery Deferred advantages?

Question

 $.ajax("example.php").done(function ()
 {
     alert(...);
 }).fail(function ()
 {
     alert(...);
 }).always(function ()
 {
      alert(...);
 });

vs

  $.ajax("example.php",

      success: function ()
      {
          alert('');
      },
      error: function ()
      {
          alert('');
      },
      complete: function ()
      {
          alert('');
      }
  );

Sorry , I can't see any advantages

Can you please explain ?

Or maybe can you give me example of the former which cant be accomplished by the latter...?

Answer 1

For starters, the second code block isn't even syntactically valid. I'd call that an advantage of the first :P

---

But in all seriousness:

It's just a different syntax for achieving the same end result. One immediate advantage is that you can wire up multiple functions for each outcome with deferred:

$.get("example.php").done(function ()
{
    alert("success 1");
}).done(function ()
{
    alert("success 2");
});

otherwise you'd have to do it like so:

function done1()
{
    alert('success 1');
}
function done2()
{
    alert('success 2');
}

$.ajax('example.php',
{
    success: function ()
    {
        done1.apply(this, arguments);
        done2.apply(this, arguments);
    }
});

---

Other advantages, quoted from How can jQuery deferred be used?

• Deferreds are perfect for when the task may or may not operate asynchronously, and you want to abstract that condition out of the code.
• ...Fetching data from multiple sources. In the example below, I'm fetching multiple, independent JSON schema objects used in an existing application for validation between a client and a REST server. In this case, I don't want the browser-side application to start loading data before it has all the schemas loaded. $.when.apply().then() is perfect for this.
• A deferred can be used in place of a mutex. This is essentially the same as the multiple ajax usage scenarios.