Two Async Javascript Functions with Parameters

Question

My question totally depends on a previous question:

Regarding approach number 3 (the "counter" one): If handleCompletion needs a value from startOtherAsync in order to do its job. How can we implement that?

Note that that value coming from startOtherAsync (probably a parameter) will make startAsync sad and unable to call handleCompletion anymore.

sounds to me like you'd want to use promises via jQuery's Deferred object. — zzzzBov
– zzzzBov, Commented Jan 28, 2014 at 2:54
Maybe that's right. I'm looking into it, I haven't used it before. — yazanpro
– yazanpro, Commented Jan 28, 2014 at 2:59
Also, can you explain what value needs to be passed from startOtherAsync? — Ja͢ck
– Ja͢ck, Commented Jan 28, 2014 at 3:31
@Jack: Technically startOtherAsync will pass nothing. but the success of his ajax call will call back handleCompletion passing the returned ajax value. — yazanpro
– yazanpro, Commented Jan 28, 2014 at 3:42

Josh · Accepted Answer · 2014-01-28 03:45:34Z

2

This is actually a perfect place to use promises. All the jQuery Ajax calls return promises by default which means you can simply chain them together:

$.ajax({/*snip*/}).then(
   function(result){

      doSomethingWithResult(result);

      return $.ajax({/*snip*/});

   }).then(function(result){

      doSomeFinalProcessing(result);

   });

And of course, a jsFiddle to demonstrate this happening.

Here is an updated fiddle that shows how to combine multiple simultaneous promises and combine their results.

http://jsfiddle.net/jwcarroll/U3N9u/

And the code:

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min);
}

function doStuffLater(msg){
    var def = $.Deferred();

    setTimeout(function(){

        def.resolve(msg);

    }, getRandomInt(300, 1000));

    return def.promise();
}

function needsBothReturns(one, two){
    console.log({one:one, two:two});
}

var first = doStuffLater("Sent First");
var second = doStuffLater("Sent Second");

$.when(first, second).done(function(result1, result2){
    needsBothReturns(result1, result2);
});

edited Jan 28, 2014 at 3:45

answered Jan 28, 2014 at 3:14

Josh

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3 Comments

yazanpro Over a year ago

It looks like this implements a callback chain not separate async functions with a third waiting function.

Josh Over a year ago

@yazanpro - If you look at the fiddle, each call to doSomething later is indeed asynchronous. You can also create your own deferred if you need to execute to things simultaneously.

yazanpro Over a year ago

Yeah, That's pretty clear now. It addresses my problem and I realized the concept as well. Thank you for your update.

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