call a function after the setTimeout finishes execution- Javascript

Question

I have a scenario where I want to call the function d() after the execution of three functions a(), b(), c(), These three functions executes parallely.

setTimeout(function a(){ alert("Hello A"); a()}, 3000);
setTimeout(function b(){ alert("Hello B"); b()}, 3000);
setTimeout(function c(){ alert("Hello C"); c()}, 3000);

After getting all the functions executed I want the below function d() to get executed

function d(){
console.log('hello D')
}

Any help would be appreciated.

Possible duplicate of [How should I call 3 functions in order to execute them one after the other?](https://stackoverflow.com/questions/5187968/how-should-i-call-3-functions-in-order-to-execute-them-one-after-the-other) — Jeremy Thille, Feb 19 '18 at 12:35

score 9 · Accepted Answer · edited Feb 19 '18 at 13:08

9

You can do this like

var promise1 = new Promise(function(resolve, reject) {
    setTimeout(function a(){ alert("Hello A"); resolve();}, 3000);
})

var promise2 = new Promise(function(resolve, reject) {
    setTimeout(function b(){ alert("Hello B"); resolve();}, 3000);
})

var promise3 = new Promise(function(resolve, reject) {
    setTimeout(function c(){ alert("Hello C"); resolve();}, 3000);
})

Promise.all([promise1, promise2, promise3]).then(function() {
  function d(){
     console.log('hello D') 
  }
  d(); 
});

edited Feb 19 '18 at 13:08

Durga

15,263
2
28
52

answered Feb 19 '18 at 12:49

Kiran Shinde

5,732
4
24
41

damn, same answer, 10 seconds apart – Jeremy Thille Feb 19 '18 at 12:50
@JeremyThille beat you :D – Kiran Shinde Feb 19 '18 at 12:51
Let's say that you provided the ES5 solution and I provided the ES6 one :) – Jeremy Thille Feb 19 '18 at 12:52
Yeah!! true that – Kiran Shinde Feb 19 '18 at 12:53
Have you checked, you are calling the same function inside? – Durga Feb 19 '18 at 12:55

score 3 · Answer 2 · answered Feb 19 '18 at 12:49

You can use Promise.all to do that.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

const a = new Promise( (resolve, reject) => setTimeout( () => {
     console.log("a is finished");
     resolve()
    }, 3000) ),
   b = new Promise( (resolve, reject) => setTimeout( () => {
     console.log("b is finished");
     resolve()
    }, 1000) ),
   c =  new Promise( (resolve, reject) => setTimeout( () => {
     console.log("c is finished");
     resolve()
    }, 2000) )

const d = () => console.log('hello D')

Promise.all( [a,b,c] ).then(d)

A. Denis · Answer 3 · 2018-02-19T12:55:11.063

1

You probably need some global variable/object to save state of executed each function and check at the end if you can start d function. Example:

// you probably need some global variable/object
oCheckedFunctions = { a:false, b:false, c:false };
function d(){
 alert('hello D')
}
function a(){ 
 alert("Hello A"); 
 oCheckedFunctions.a = true;
 checkAndTryForD();
}
function b(){ 
 alert("Hello B"); 
 oCheckedFunctions.b = true;
 checkAndTryForD();
}
function c(){ 
 alert("Hello C"); 
 oCheckedFunctions.c = true;
 checkAndTryForD();
}

function checkAndTryForD() {
 if (oCheckedFunctions.a && oCheckedFunctions.b && oCheckedFunctions.c) {
  d();
 }
}

// your functions
setTimeout(a, 3000);
setTimeout(b, 3000);
setTimeout(c, 3000);

edited Feb 19 '18 at 12:55

answered Feb 19 '18 at 12:51

A. Denis

562
7
15

3

Granted, this works, but there are more elegant ways to do it. – Jeremy Thille Feb 19 '18 at 12:53
1

... and async/await :) https://hackernoon.com/6-reasons-why-javascripts-async-await-blows-promises-away-tutorial-c7ec10518dd9 – Jeremy Thille Feb 19 '18 at 12:59

score 1 · Answer 4 · answered Feb 19 '18 at 12:53

1

Just define a promising timer once:

 const timer = ms => new Promise(res => setTimeout(res, ms));

So you can do:

 const log = v => _ => console.log(v);

 Promise.all([
  timer(3000).then(log("a")),
  timer(3000).then(log("b"))
 ]).then(log("c"));

answered Feb 19 '18 at 12:53

Jonas Wilms

132,000
20
149
151

call a function after the setTimeout finishes execution- Javascript

4 Answers4