How to block on asynchronous functions in JavaScript

Question

I need to write a function in JavaScript, which returns a state from calling an asynchronous function. However, the caller only receives the value and no callback function is to be provided. I tried something like:

function getState() {
    var ret = null;
    asyncCall("request",
        function() { ret = "foo"; } // callback
    );
    while (ret === null)
        ; // block on the asynchronous call
    return ret;
}

However, the loop is never going to end…

Any ideas? Thank you.

Answer 1

Why not just:

asyncCall("request", function() {
    // here you can inspect the state
});

What's the point of the wrapper function?

Asynchronous functions work this way. If you want to block the execution, then use a synchronous call:

var state = syncCall("request");

Answer 2

I think you're looking for StratifiedJS, http://stratifiedjs.org It allows you to "orchestrate" your async code exactly like you wrote, BEWARE that it "writes" like synchronous code, it will NOT block the rest of your application. You can use it anywhere by loading the apollo js library.

This is how it would look like in Stratified JavaScript:

function getState() {
  waitfor (var ret) {
    // block on the asynchronous call
    asyncCall("request", resume);
  }
  return ret;
}

of course there are modules/libraries that would just make it look like this: http://onilabs.com/modules#http

function getState() {
  return http.get("request");
}