How to control setTimeout with promises

Question

var functionsArray = [
  function() {
        setTimeout(function() {
        console.log(1);
    }, 100);
  },
  function() {
    setTimeout(function() {
        console.log(2);
    }, 200);
  },
    function() {
        setTimeout(function() {
            console.log(3);
    }, 10);
  }
],

Say I have an array of functions like above(the number of functions in it is not known). I want to write a function which takes this array as parameter and executes them in sequence. In the example above, I want it to log 1,2,3 in the sequence. Since Promise.all does not guarantee the order of execution, is it possible to achieve this without callback hell?

in the first instance, create functions that actually return promises... — Alnitak, Sep 30 '20 at 13:39
This: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/Promise — Randy Casburn, Sep 30 '20 at 13:45
Does this answer your question? [Resolve promises one after another (i.e. in sequence)?](https://stackoverflow.com/questions/24586110/resolve-promises-one-after-another-i-e-in-sequence) — Maxwell s.c, Sep 30 '20 at 17:28

Alnitak · Accepted Answer · 2020-09-30T14:45:38.223

You can't get a promise from a function that just calls setTimeout - it needs some help, e.g.:

function after(n, f) {
  return () => new Promise(resolve => {
    setTimeout(() => {
        resolve(f());
    }, n);
  });
}

with usage:

var functionsArray = [
  after(100, () => console.log(1)),
  after(200, () => console.log(2)),
  after( 10, () => console.log(3)),
];

With that array you can then just await each function in turn:

for (let f of functionsArray) {
  await f();
}

Maxwell s.c · Answer 2 · 2020-09-30T13:54:24.940

-1

You can write an simple setTimeoutPromise function:

function timeoutPromise(time = 0){
  return new Promise(resolve => setTimeout(resolve, time)
} 


await timeoutPromise(10);
console.log('waited 10 sec')
timeoutPromise(20).then(() => console.log('waited 20 sec')

//make a new array as you like

Promise.all([
 timeoutPromise(100).then(() => console.log(1)),
 timeoutPromise(200).then(() => console.log(2)),
 timeoutPromise(300).then(() => console.log(3))
])

edited Sep 30 '20 at 13:54

answered Sep 30 '20 at 13:52

Maxwell s.c

1,583
15
29

this doesn't answer the question (which requires an _array_ of functions) – Alnitak Sep 30 '20 at 13:53
@Alnitak i've updated it, but you need to specify how exactly you want your functions to be stored or work to get a better answer – Maxwell s.c Sep 30 '20 at 13:54
It wasn't my question, but your use of `Promise.all` still doesn't resolve the fundamental question which was that the OP wants the functions to be called _in sequence_. – Alnitak Sep 30 '20 at 14:38
NB: this is why my answer uses a function that returns a function that in turn returns a Promise - your version instantiates all three Promises (and invokes the setTimeout calls) immediately. – Alnitak Sep 30 '20 at 15:00

How to control setTimeout with promises

2 Answers2

Linked