An implementation of reduce modeled after the underscore.js api that does not default to Array.prototype.reduce.

reduce.js

function reduce(obj, iterator, memo, ctx) {
	var keys = Object.keys(obj),
	memo = memo || obj[keys[0]];
	ctx = ctx || null;
	for (var i = arguments[2] ? 0 : 1; i < keys.length; i++)
		memo = iterator.call(ctx, memo, obj[keys[i]], keys[i], obj);
	return memo;
}