Memoize for Javascript

I wrote a memoize function for Javascript today to cache file timestamps. I thought I would share it with the world. Here is the code:

function memoize(f){
    var cache = {}
    return function(){
        var keys = []
        for (var i = 0; i < arguments.length; i++){
            keys.push(typeof(arguments[i]) + ':' + String(arguments[i]))
        var key = keys.join('/')
        if (key in cache){
            return cache[key]   
            var val = f.apply(null, arguments)
            cache[key] = val
            return val

Let's say you have a function:

function f(x, y){
  return x + y * 2

If you memoize it:

f = memoize(f)

The first time you call f with arguments (3, 4):

f(3, 4) => 11

It will compute it, but the second time:

f(3, 4) => 11

It will merely return the cached value computed from the last time.

Note about the implementation: the equality metric used by this memoize function is: 2 objects are equal iff they are of the same type:

typeof(one) == typeof(other)

and, they have the same string represention:

String(one) == String(other)

That is it. Enjoy!

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