memorize.js

function sum() {
	var res = 0,
		i = 0,
		len = arguments.length;
	for (;i < len; i++) {
		res += arguments[i];
	}
	console.log('Sum called', res);
	return res;
}

function mul() {
	var res = 0,
		i = 0,
		len = arguments.length;
	for (;i < len; i++) {
		res += arguments[i];
	}
	console.log('Mul called', res);
	return res;
}

function safeArgs(func) {
	if (arguments.length !== func.length) {
		throw 'Wrong numbe of arguments';
	}
	return func.apply(window, arguments);
}
  
function memorize(f) {
	if (!f.cache) f.cache = {};
	return function() {
		var cacheId = [].slice.call(arguments).join('');
		console.log(this);
		return f.cache[cacheId] ?
				f.cache[cacheId] :
				f.cache[cacheId] = f.apply(window, arguments);
	};
}

var mSum = memorize(sum);
mSum(1,2)
mSum(1,2)
mSum(1,2)
mSum(1,2)
mSum(1,2)