Break statement not exiting all nested loops within JavaScript

Question

I am having the understanding that break statement terminates all nested loops. I have written the following code and it is not working as expected.

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

Actual Output:

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
2*4
4*0
4*1
4*2
4*3
4*4

As per my understanding, the output should not include 4*0...4*4 because when i == 3, the break should terminate all nested loops.

Expected Output:

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
2*4

It terminates in the loop it is in, it is not terminating the outerloop. Working as expected. If you moved it before the for (j...., you would get what you were expecting. — epascarello
– epascarello, Commented Mar 31, 2020 at 19:51

Matti Greff · Accepted Answer · 2020-03-31 19:57:35Z

10

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

answered Mar 31, 2020 at 19:57

Matti Greff

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1 Comment

MaKham Over a year ago

OH this is the best solution than many spaghetti code comment

Paweł · Accepted Answer · 2020-03-31 20:01:11Z

1

Why don't you place a break in the first loop?

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

answered Mar 31, 2020 at 20:01

Paweł

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Comments

user13124036 · Accepted Answer · 2020-03-31 19:53:44Z

0

No, break only breaks the current loop, not all of them. You can use a boolean variable to break out of the enclosing loop as well.

Example:

<script>
    let break = false
    for (i = 0; i < 5; i++) {
        for (j = 0; j < 5; j++) {
            if (i == 3) {
                break = true;
                break;
            }
            document.write(i + '*' + j + '<br>');
        }
        if(break) break
    }
</script>

answered Mar 31, 2020 at 19:53

user13124036

Comments

anees · Accepted Answer · 2020-03-31 19:57:39Z

0

By default the only innermost loop is escaped but you can achieve the behaviour you are expecting by a self enclosing function and a return statement.

(function(){
    for (i = 0; i < 5; i++) {
        for (j = 0; j < 5; j++) {
            if (i == 3) {
                return;
            }
            document.write(i + '*' + j + '<br>');
        }
    }
})()

answered Mar 31, 2020 at 19:57

anees

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