Breaking out of JavaScript 'For' Loop using False?

Question

I didn't know this was possible (is it?)

The below code apparently logs values 1 to 5, then breaks out of the 'for' loop, because the 'false' value is returned.

function x() {
    for (var i = 0; i < 10; i++) {
        console.log(i);
        if (i == 5) return false;
    }
    return true
}

console.log(x());

My question is:

• How come the for loop short-circuits when 'false' is returned? I looked at MDN but there is nothing there about using 'false' to break out of the for loop. Also tried looking at ECMA specs, but sadly too noob.

• Why doesn't the function return 'true' to the console, as the 'return true' statement exists after the 'for' loop is executed? Even if false somehow returns 'first', shouldn't 'true' return last or also?

Answer 1

return false is not breaking your loop but returning control outside back.

function x() {
    for (var i = 0; i < 10; i++) {
        console.log(i);
        if (i == 5) return false;
    }
    return true
}

console.log(x())

Output:

0
1
2
3
4
5
false //here returning false and control also 

Where break will break your loop instead of coming out from function.

function x() {
    for (var i = 0; i < 10; i++) {
        console.log(i);
        if (i == 5) break;
    }
    return true
}

console.log(x())

Will output:

0
1
2
3
4
5 //after this loop is breaking and ouputing true
true 

Answer 2

The return statement ends the function , so the return true line is unreachable. Hope that helps.