Is it possible to create my own async Javascript code

Question

I wish to validate my assumptions:

As I read yet, to create an async call, I must eventually end up calling a javascript native call (like setTimeout() || XMLHttpRequest() || ...) to get out of the engine main scheduler loop.

Any third party library wishing to be async, will indirectly do the same.

Is this right, or is there a way to create my own async code (for instance by allowing a blocking feature on my code) intentionally without a js native call ?

WebWorker could offer a way. Depends, if you regard them as native calls. — Sirko, Nov 12 '14 at 20:14
...what exactly are you asking? The question in your post title is different than the ones you're asking in your question's description, if I understand correctly — elzi, Nov 12 '14 at 20:14
to be clear: JS itself provides no way of doing async anything (afaik), you have to use something provided by the host environment, like setTimeout or ajax. — dandavis, Nov 12 '14 at 20:25

Don Rhummy · Accepted Answer · 2014-11-12T20:46:11.360

2

In JavaScript, there are a few ways to write code that can be run asynchronously. Typically the methods used were:

setTimeout
setInterval
XMLHttpRequest

But in HTML5 (and beyond) there are a lot of other methods that work asynchronously. For example, the new asynchronous file uploading, Web Workers and Promises. (NOTE: not all of these are supported by every browser)

Your question, though, is vague. What are you attempting to do? If it's UI-centric, you may want to look at requestAnimationFrame

If by blocking, you mean you want to show a "loading" gif and then go do stuff and change that after the "stuff" is done, there are a lot of ways to handle that but with the newer browsers, you'd use Promises: http://www.html5rocks.com/en/tutorials/es6/promises/ with a check for some value in a timeout function.

//The value to check
var isDone = false;

var asynchCheck = function(resolve, reject) {

    if ( notStarted )
    {
         // do stuff (calls async function that eventually sets "isDone" = true)
    }

    if ( isDone === true )
    {
        if ( no errors ) resolve("Stuff worked!");
        else reject(Error("It broke"));
    }

    //Check again
    else setTimeout( asynchCheck, 50 );
}
//Start your function
var promise = new Promise(asynchCheck);

//Now set the success/fail functions
promise.then(function(result) {
  console.log(result); // "Stuff worked!"
}, function(err) {
  console.log(err); // Error: "It broke"
});

edited Nov 12 '14 at 20:46

answered Nov 12 '14 at 20:17

Don Rhummy

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promises alone can't create async, you still need an async interface to wrap. – dandavis Nov 12 '14 at 20:26
@dandavis http://stackoverflow.com/questions/12683510/ios-6-safari-setinterval-doesnt-get-fired I can't find it now but there's also an issue on mobile browsers if your `setInterval` delay is too short. – Don Rhummy Nov 12 '14 at 20:36
@dandavis I removed it but I ran into issues recently on iOS with setInterval, just can't remember what they were – Don Rhummy Nov 12 '14 at 20:46
@Don, my question is vague cause it apply to javascript in general. However, I am actually studying the promises/a+, and I am trying to do async without setTimeout or any native call. I cannot seem to find any custom made async call I could construct on my own, except by eventually using a js native call, eventually. If no more answer, I will accept your answer. – Alain Nov 13 '14 at 01:33
1

@Alain read about threading in JavaScript and you'll see the reason you can't do async without those native calls is because JavaScript is single threaded. – Don Rhummy Nov 13 '14 at 04:43

Is it possible to create my own async Javascript code

1 Answers1