在setTimeout完成执行后调用函数-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.

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(); }); 

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

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); 

Answer 4

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"));