Javascript Promises: Chain same promise n times, then do something else

Question

I have a promise-returning function that does some async stuff, let's call it functionToRepeat().

I am trying to write the function repeatFunction(amount) , so that it will start the promise, wait for completion, start it again, wait for completion, and so on a given amount of times. This repeatFunction(amount) should also be thenable, so that I can chain other stuff after it's been executed.

Here is my attempt:

function functionToRepeat(){
  let action = new Promise(function(resolve,reject){
    setTimeout(function(){
      console.log("resolved!");
      resolve()}
    ,1000);
  })
  return action
}

function repeatFunction(amount) {
  if(amount==0){
    return Promise.resolve();
  }
  return functionToRepeat().then(function(){
    repeatFunction(amount-1);
  });
}

repeatFunction(5).then(function(){
 console.log("DONE!");
})

This successfully chains my promises (or so it seams, I get one "resolved!" per second in the console). However the .then() I try to chain after my repeatFunction(5) happens after the 1st promise ends, not after all 5 have ended!

So in my console I get:

resolved! DONE! resolved! resolved! resolved! resolved!

What am I doing wrong and what should I change?

Answer 1

How about simply:

function repeat(func, times) {
  var promise = Promise.resolve();
  while (times-- > 0) promise = promise.then(func);
  return promise;
}

When tested with this:

function oneSecond() {
  return new Promise(function (resolve, reject) {
    setTimeout(function () {
      console.log("tick");
      resolve();
    }, 1000);
  });
}

repeat(oneSecond, 5).then(function () {
    console.log("done");
});

this output is produced over 5 seconds:

tick
tick
tick
tick
tick
done