Early exit from function in a forEach?

Question

How can I early exit from a function in my TypeScript file?

checkIfFollowed(){
    
    this.currentUserInfos.followed.forEach(element => {
        if(18785 == 18785){
            console.log('its true');                
            this.alreadyFollowed = true;
            return; // Exit checkIfFollowed() here
        }

    });

    this.alreadyFollowed = false;
    console.log('the end');
    return;
}

When I'm running it, it's executed completely, but it should exit after the first:

'its true'

But in my console, I get:

its true

its true

the end

Foreach loops 2 times as expected, but why the method doesn't stop after hitting a "return"?

I'm not trying to get out of the forEach, but ending the method 'checkIfFollowed' in the foreach.

'the end' should not be printed.

There's 2 objects in currentUserInfos.followed It's just a nested object, nothing special — Toodoo, Apr 03 '17 at 08:33
Use Array#some from here :https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Array/some — Partha Sarathi Ghosh, Apr 03 '17 at 08:36
What is the actual requrement? You are hard coding the if check here as `if(18785 == 18785)`. I dont think this is your actual requirement. — Partha Sarathi Ghosh, Apr 03 '17 at 08:42
@echonax, thanks for your answer, but it's not. i'm trying to exit checkIfFollowed method, not only the forEach. — Toodoo, Apr 03 '17 at 09:05
@Toodoo the reason you can't exit `checkIfFollowed` is that you can't exit `forEach` — eko, Apr 03 '17 at 09:27
Yup, didn't get it, but thanks to @gsc i got it now ! Thanks for your help echnoax ! — Toodoo, Apr 03 '17 at 09:29

score 7 · Accepted Answer · answered Apr 03 '17 at 09:10

7

Another approach, with for loop:

checkIfFollowed() {
  for (let i = 0; i < this.currentUserInfos.followed.length; ++ i) {
    if (18785 == 18785) {
      console.log('its true');                
      this.alreadyFollowed = true;
      return; // exit checkIfFollowed() here
    }
  }

  this.alreadyFollowed = false;
  console.log('the end');
  return;
}

answered Apr 03 '17 at 09:10

gsc

1,559
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It works. Weird, why it doesn't work with forEach approach ? Many thanks. – Toodoo Apr 03 '17 at 09:14
3

Because using `forEach`, you are entering a new function (`.foreach(function (e) {…})`) and calling `return` there stops that new function and not the parent (`checkIfFollowed`) one. You are welcome! – gsc Apr 03 '17 at 09:15

Vivek Doshi · Answer 2 · 2017-04-03T09:11:52.813

5

Try this instead of forEach

.every() (stops looping the first time the iterator returns false or something falsey)

With every():

checkIfFollowed(){

        this.currentUserInfos.followed.every(function(element, index) {
            // Do something.
            if (18785 == 18785){
                console.log('its true');                
                this.alreadyFollowed = true;
                return false;
            }
        });
        if(this.alreadyFollowed) 
        {
            return ;
        }
        this.alreadyFollowed = false;
        console.log('the end');
        return;
}

edited Apr 03 '17 at 09:11

answered Apr 03 '17 at 08:31

Vivek Doshi

56,649
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Thanks for your answer. When I try this, the 'return' breaks the loop, but doesn't end the method. – Toodoo Apr 03 '17 at 08:36
It returns same output? – Vivek Doshi Apr 03 '17 at 08:36
Try now , forgot to return false; – Vivek Doshi Apr 03 '17 at 08:37
Here iteration of method will not stop. But you can restrict the execution of some line of code by `if` check. But I think it is better to use `some` rather `forEach` – Partha Sarathi Ghosh Apr 03 '17 at 08:39
.every() (stops looping the first time the iterator returns false or something falsey) – Vivek Doshi Apr 03 '17 at 08:41
.some() (stops looping the first time the iterator returns true or something truthy) – Vivek Doshi Apr 03 '17 at 08:41
Thanks @ParthaSarathiGhosh , updated my answer with both. – Vivek Doshi Apr 03 '17 at 08:44
@Toodoo , Will you please check now ? – Vivek Doshi Apr 03 '17 at 08:50
@VivekDoshi it's end the loop but not the function :/ – Toodoo Apr 03 '17 at 08:53
Will you please explain , what do you want exactly ? – Vivek Doshi Apr 03 '17 at 09:08
Its there now, please have a look @Toodoo – Vivek Doshi Apr 03 '17 at 09:12
It seems we can't do it with forEach or every. @gsc got the answer. Thanks for your help – Toodoo Apr 03 '17 at 09:22

score 2 · Answer 3 · answered Apr 03 '17 at 09:13

You could also not fight foreach :) and do it this way:

checkIfFollowed(){

    const filtered = this.currentUserInfos.followed
       .filter(el => el.id === 18785) // or some other condition
       .forEach(element => {
         // maybe you don't need to do anything here
         // or you can continue processing the element and you know you only have 
         // items that you want
      });

   this.alreadyFollowed = filtered.length > 0;
   console.log('the end');
//    return; // no need for an empty return at the end of a function.
}

HTH

Early exit from function in a forEach?

3 Answers3