How do I make my function as asynchronous in Javascript?

Question

I am trying to understand the async behaviour of Javascript, how can we implement in normal functions. For example below code I am trying to implement a custom SetTimeout function which would work asynchronously. It should call the function muCsutSetInterval and go the console.log("after");.

Please suggest the right way to do it. Appreciate your help..

var myCustSetInterval = function (time, callback){
    let initial = new Date();
    let current;
    while(true){
        current = new Date();
        if(current.getTime()-initial.getTime()===time){
            break;
        }
    }
    callback();
}

console.log("before");

myCustSetInterval(5000,()=>{
    console.log("Callback");
});

console.log("after");

javascript is synchronous. To get asynchronous results, you have to rely on [apis](https://nodejs.org/api/index.html) that aren't bound by that rule. — Kevin B, Apr 03 '18 at 18:34
@Igor - I'm probably wrong, but I don't think that is what the OP is asking. I believe the OP is interested in understanding the use of Async/Await along with Promise objects. — Randy Casburn, Apr 03 '18 at 18:36
@RandyCasburn - maybe. I do not see any reference to either keyword async/await in the question though. — Igor, Apr 03 '18 at 18:39

score 1 · Answer 1 · edited Apr 03 '18 at 19:22

1

You cant write asynchronous javascript. However the javascript API provides internal functions (setTimeout, fetch) that behave asynchronously, which you can work with. So you need those async internal calls to actually write async code. E.g.:

function customSetTimeout(callback, ms, ...args) {
  const ends = Date.now() + ms;
  (function check() {
     if(new Date >= ends) {
       callback(...args);
     } else {
       setTimeout(check, 0); // <- the internal call
     }
  })()
}

edited Apr 03 '18 at 19:22

rtn

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answered Apr 03 '18 at 18:37

Jonas Wilms

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Why are people downvoting this? Perfectly valid answer. – rtn Apr 03 '18 at 19:22

How do I make my function as asynchronous in Javascript?

1 Answers1