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

Besides what you have already stated the main downside I see is that a "return" statement will work differently. (Which is often why I end up using "for" over "$.each" many times in my own ventures.)

Answer 2

It seems pretty valid. I honestly don't think that performance would decrease too much. But there is however one big downside, that is easily fixable: the break statement.

function repeat(n, f) {
   for (var i = 0; i < n; i++) {
      var tcall=i;
      tcall.die=function(){i=n}
      f.call(tcall);
   }
}  

This way you would be able to call this.die() instead of break; which I think would throw an error.

Answer 3

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);
});

Answer 4

You say you want a revolution... Well, you know: ruby did it just before (?)

Number.prototype.times = function(func) { 
    for(var i = 0; i < Number(this); i++) {
        func(i); 
    }
}

means

(50).times(function(i) {
    console.log(i)
})

Anyway, don't fight against C, you'll always lose :-P

Answer 5

it's an interesting thought, but if you dislike the syntax for the loop, you could always do a different type of loop:

var i = arr.length; 
while (i--) {
    // do stuff
}

the reverse while loop is generally faster than a for loop as well.