Question

Is there some framework similar to underscore that allows me to run async methods on collections.

Something like _.each(collection, itemCallback, doneCallback).

For example:

_.each(items, function(item, token){
    item.someProperty = null;
  }, function(err){
     console.log("The loop is done");
  });

Edit: async.js actually doesn’t solve the problem. For example the following code

<script type="text/javascript" src="async.js"></script>
<script type="text/javascript">

var arr = ["a","b","c"];

async.forEach(arr, function(item, met){
    console.log(item);
},
function(err){
});
console.log("Done");

</script>

prints a b c Done

While I want it to print Done a b c

I can do it with underscore deffer but maybe there is some other lib that can do it without wrappers.

Answer 1

Async.js module will do the trick. Your example is just too fast for you to fully notice it is actually working as you will expect. Here is an example with a small delay added so you can notice the actual order of execution:

async.each([0,1,2,3,4,5,6,7,8,9], function(item, callback) {
  setTimeout(function() {
    console.log('>', item);
    callback();
  }, 2 * Math.random() * 1000);
}, function(err) {
  console.log('> done');
});

console.log(':)');

And the output:

:)
> 4
> 5
> 2
> 7
> 8
> 3
> 0
> 1
> 9
> 6
> done

Also, to really do it asynchronous you might consider to use Web Workers; but for now Async.js provides you a really simple way to do something similar (but not actual Web Workers) named queue:

var q = async.queue(function(item, callback) {
  setTimeout(function() {
    console.log('>>', item);
    callback();
  }, 2 * Math.random() * 1000);
}, 5);

q.drain = function() {
  console.log('>> done');
};

q.push([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

console.log('B)');

And the output:

B)
>> 1
>> 2
>> 5
>> 6
>> 4
>> 3
>> 0
>> 7
>> 8
>> 9
>> done

And if finally you run both simultaneously, here is an example of the output:

:)
B)
>> 2
> 3
>> 4
>> 1
> 8
>> 6
> 7
> 1
> 4
>> 3
> 0
> 2
>> 7
>> 5
> 6
> 5
> 9
> done
>> 8
>> 0
>> 9
>> done