What's the Best Way to Break from Nested Loops in JavaScript

What's the best way to break from nested loops in JavaScript?

Just like Perl,

loop1:
    for (var i in set1) {
loop2:
        for (var j in set2) {
loop3:
            for (var k in set3) {
                break loop2;  // breaks out of loop3 and loop2
            }
        }
    }

as defined in EMCA-262 section 12.12. [MDN Docs]

Unlike C, these labels can only be used for continue and break, as Javascript does not have goto.

How to break nested loops in JavaScript?

You should be able to break to a label, like so:

function foo () {
    dance:
    for (var k = 0; k < 4; k++) {
        for (var m = 0; m < 4; m++) {
            if (m == 2) {
                break dance;
            }
        }
    }
}

How do I break out of nested loops in Java?

Like other answerers, I'd definitely prefer to put the loops in a different method, at which point you can just return to stop iterating completely. This answer just shows how the requirements in the question can be met.

You can use break with a label for the outer loop. For example:

public class Test {
    public static void main(String[] args) {
        outerloop:
        for (int i=0; i < 5; i++) {
            for (int j=0; j < 5; j++) {
                if (i * j > 6) {
                    System.out.println("Breaking");
                    break outerloop;
                }
                System.out.println(i + " " + j);
            }
        }
        System.out.println("Done");
    }
}

This prints:

0 0
0 1
0 2
0 3
0 4
1 0
1 1
1 2
1 3
1 4
2 0
2 1
2 2
2 3
Breaking
Done

Break statement not exiting all nested loops within JavaScript

You have to specify which loop you are breaking from.

loop1: for (i = 0; i < 5; i++) {
    loop2: for (j = 0; j < 5; j++) {
        if (i == 3) {
            break loop1;
        }
        document.write(i + '*' + j + '<br>');
    }
}

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/break

Breaking out of an outer loop from an inner loop in javascript

Depending on what your conditionals are, it should be easy to set the iterator of your for-loop to something that would break it, and set your while condition to false. For example,

while(someBoolean){
    for(var i = 0; i < size; i++){
        if(wantToBreak){
            i = size;
            someBoolean = false;
        }else{
            //Do Stuff
        }
    }
}

Breaking out of nested loops

It has at least been suggested, but also rejected. I don't think there is another way, short of repeating the test or re-organizing the code. It is sometimes a bit annoying.

In the rejection message, Mr van Rossum mentions using return, which is really sensible and something I need to remember personally. :)

breaking a nested loop

We can get this down to a one-liner, and it will do the early exit you want:

bool walletContainsUtilityToken = Wallets.Any(w => ExchangeFunctions.UtilityTokens.Any( ut => ut == w.Currency));

This one might be easier to understand (no nesting, only one -shorter- lambda):

bool walletContainsUtilityToken = Wallets.Select(w => w.Currency).Intersect(ExchangeFunctions.UtilityTokens).Any();

Taking the second option, for clarity I'd actually write it like this:

bool walletContainsUtilityToken = Wallets.
    Select(w => w.Currency).
    Intersect(ExchangeFunctions.UtilityTokens).
    Any();

If you really want to continue using the full loop, I'd add a check to the loop conditions like so:

bool walletContainsUtilityToken = false;
for(int i = 0; i < Wallets.Length && !walletContainsUtilityToken; i++)
{
    foreach (Currency ut in ExchangeFunctions.UtilityTokens)
    {
        if (Wallets[i].Currency.Equals(ut))
        {
            walletContainsUtilityToken = true;
            break;
        }
    }
}

Finally, if these lists are large you could significantly improve performance by pre-arranging them into data structures for faster lookup (ie: a Dictionary, or even something that would support a binary search). But this is only a win if the lists are large enough.

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