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.

• Jeremy Thille: Possible duplicate of How should I call 3 functions in order to execute them one after the other?
• Shikha thakur: @JeremyThille Nope, Its different.

Answer 1

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(); 
});

• Jeremy Thille: damn, same answer, 10 seconds apart
• Kiran Shinde: @JeremyThille beat you :D
• Jeremy Thille: Let's say that you provided the ES5 solution and I provided the ES6 one :)
• Kiran Shinde: Yeah!! true that
• Durga: Have you checked, you are calling the same function inside?

Answer 2

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)

Answer 3

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"));

Answer 4

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);

• Jeremy Thille: Granted, this works, but there are more elegant ways to do it.
• Jeremy Thille: ... and async/await :) hackernoon.com/…