在for循环完成后，是否可以使用Deferred对象来创建回调？

Question

I have a for loop which fades in each li, what I want to do is wait until the very last li has fully faded in and then continue with the code similar to a callback but I'm unsure how to achieve this? I was thinking that I could possibly use a Deferred object?

JS

  var newArray = [3,2,6,4,0,1,5];
    for (var i = 0; i < newArray.length; i++) {
      var dfd = $.Deferred();
      $(this).eq(newArray[i]).fadeIn(i * 500);
      dfd.resolve();
      //.. continue with callback code??
    }

Answer 1

You can use $.when : by passing the Deferreds from all your fadeIn calls to it, you can register a callback to be executed only when all of them are done:

var deferreds = [];
for (var i = 0; i < newArray.length; i++) {
    var dfd = $(this).eq(newArray[i]).fadeIn(i * 500);
    deferreds.push(dfd);
}
$.when.apply($, deferreds).then(function() { ... });

Working example at jsFiddle . Note that you can use the return value of fadeIn as a Deferred .

Update: since you want each fadeIn to start only after the last one ended, Bergi's answer might be more appropriate. An alternative (simpler, IMHO) could be:

var i = 0;
function f() {
    if ( i < newArray.length ) {
        $(this).eq(newArray[i]).fadeIn(i * 500, f);
        i++;
    } else {
        // Your "done" callback, if any
    }
}
f();

Working example . I stuck to your original code (each effect using a different duration), but if you want all them to have the same one, remove the i * and just use 500 .

Answer 2

I don't think Deferreds will be of great help here. Surely, you can get a .promise() for every [effect] queue on jQuery instances, and because of that method you could even pass jQuery objects right into $.when , but I think a callback chain - and for successive animations you need some chain - can do it easier:

function chainedFadeIn($el, order, callback) {
    if (!order.length)
        return callback();
    $el.eq(order.shift()).fadeIn(500, function() {
        chainedFadeIn($el, order, callback); // notice we removed the first element
    }); 
}
chainedFadeIn($(this), [3,2,6,4,0,1,5], function() {
    // do something
});

Alternative version with Promises:

function getFadeInChain($el, order) {
    if (!order.length)
        return order; // or anything else
    return $el
      .eq(order.shift())
      .fadeIn(500)
      .promise()
      .then(getFadeInChain.bind(null, $el, order));
}
getFadeInChain($(this), [3,2,6,4,0,1,5]).done(function() {
    // do something
});

Demos at jsfiddle.net: callbacks , Deferred