Non-recursive Heap's Algorithm in JavaScript, with a callback

gistfile1.txt

function iterate(arr, callback) {
	var fac = [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800];
	function swap(a, b) {
		var tmp = arr[a];
		arr[a] = arr[b];
		arr[b] = tmp;
	}

	callback(arr);
	for (var iter = 1, last = fac[arr.length]; iter < last; iter++) {
		if (iter % 2) swap(0, 1);
		else if (iter % 6) swap(0, 2);
		else {
			var cycle = arr.length - 1;
			while (iter % fac[cycle] > 0) cycle--;
			var left = cycle % 2 == 0 ? 0 : (iter / fac[cycle] - 1) % (cycle + 1);
			swap(left, cycle);
		}
		callback(arr);
	}
}