JavaScript Async Map

gistfile1.js

function asyncMap(list, iterator, callback) {
	var finished = 0;
	var results = [];
	var firstErr;

	var makeIteratorFinishCallback = function(i) {
		return function(err, item) {
			finished++;
			if (err) {
				if (!firstErr) {
					firstErr = err;
					callback(err);
				}
				return;
			}
			results[i] = item;
			if (!firstErr && finished === list.length) {
				callback(undefined, results);
			}
		};
	};

	for (var i = 0; i < list.length; i++) {
		iterator(list[i], makeIteratorFinishCallback(i));
	}
}