Javascript Memoization Example from Javascript the Good Parts

memoization.js

var memoizer = function (memo, formula) { 
	var recur = function (n) { 
		var result = memo[n]; 
		if (typeof result !== 'number') { 
			result = formula(recur, n); 
			memo[n] = result; 
		} 
		return result;
	};
	return recur;
};

var fibonacci = memoizer([0, 1], function (recur, n) { 
	return recur(n − 1) + recur(n − 2);
});