JavaScript for-loop alternative: repeat(n, function(i) { … });

Question

This is the regular for-loop:

for (var i = 0; i < n; i++) { ... }

It is used to iterate over arrays, but also to just repeat some process

Answer 1

To address the issue of not having the break statement as others have mentioned, I would solve it this way:

function repeat(n, f) {
    for (var i = 0; i < n; i++) {
        if (f(i) === false) return;
    }
}

Then returning false from within a loop handler will be equivalent to break.

Another disadvantage is that the context changes. You may want to add the option of proxying a context into the loop handlers:

function repeat(context, n, f) {
    if (!f) f = n, f = context, context = window;

    for (var i = 0; i < n; i++) {
        if (f.call(context, i) === false) return;
    }
}

Now, an advantage is that the index is preserved by the function scope, to avoid a common bug:

for (var i = 0; i < 10; i++) {
    setTimeout(function () {
        alert(i); // Will alert "10" every time
    }, 1000);
}

repeat(10, function (i) {
    setTimeout(function() {
        alert(i); // Will alert "0", "1", "2", ...
    }, 1000);
});