Break while loop in array.forEach inside it?

Question

Note: I want to break the while() loop using the forEach callback function, not to break the forEach itself.

I'm currently trying to break a while loop in a forEach method inside that same while loop, but Javascript does not like break statements inside functions. It spits out unsynctatic break or illegal break statement depending on the environment.

I'm trying to do something like this:

while(true) {
    example = [false, false, true];
    example.forEach(function breakWhile(element) {
        if(element) {break;}
    })
}

I'm aware that for...of (plus using a label on the while loop) solves this, but is it really my only way out? I quite prefer using array.forEach. And even worse, I could want to use a function instead, which is also underappreciated by JS engines.

Possible duplicate of How to short circuit Array.forEach like calling break? — Void Ray
– Void Ray, Commented Sep 29, 2017 at 14:51
@VoidRay not really, I want to break the while() loop, not the forEach. — Rafael
– Rafael, Commented Sep 29, 2017 at 14:51
There are every and some that you should use here, along with several other Array methods. — Sebastian Simon
– Sebastian Simon, Commented Sep 29, 2017 at 14:52
@Rafael then you'll have to break it like any other while loop. running break in a callback certainly isn't the same as running it in the while loop. Your options are limited here. Breaking the forEach would be the first step. — user400654
– user400654, Commented Sep 29, 2017 at 15:32

Keith · Accepted Answer · 2017-09-29 15:30:03Z

3

I think your best option is just to use a flag.

let dobreak = false;
while(!dobreak) {
    example = [false, false, true, false];
    example.forEach(function breakWhile(element) {
        if(element) {dobreak = true;}
        else if(!dobreak) {
          console.log(element);
        }
    })
}

Another idea is to create a function to replace the built-in forEach, here I've called it breakForEach if you return true inside the iteration callback it will break the forEach, and also return true so you can break the while.

You could even add this to the default Array.prototype, but it's not advisable.

function breakForEach(arr, iter) {
  for(let l = 0; l < arr.length; l ++) {
    if (iter(arr[l])) return true;    
  }
  return false;
}

while(true) {
    var example = [false, false, true, false];
    if (breakForEach(example, function breakWhile(element) {
        if(element) return true;
        console.log(element);
    })) break;
}

edited Sep 29, 2017 at 15:30

answered Sep 29, 2017 at 14:57

Keith

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3 Comments

Rafael Over a year ago

Hmmm. That's not exactly what I wished (break is cleaner), but it is indeed a solution. Will wait a bit for a possible better solution before accepting this, but +1 for coming up with a solution at least. ;)

Keith Over a year ago

Is this a pattern you get regularly? If so you could maybe create a helper function,. maybe called whileForEachBreak or something like that.

Rafael Over a year ago

Actually that's the first time I had to do this. A helper function would be also less clean than just breaking with the forEach, but that doesn't seem to be a possibility.

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