A function that, given an array and a mapping function that uses a callback, calls a callback with the mapped array as a parameter

callback_map.js

var callback_map = function(arr, func, callback) {
	var rv = [];
	var waiting_for = arr.length;
	arr.forEach(function(item, index) {
		func(item, function(mapped) {
			rv[index] = mapped;
			waiting_for--;
			if(waiting_for <= 0) {
				callback(rv);
			}
		});
	});
};