Let's use a simple example, fibonacci numbers.
function fib(n) {
if (n < 2) return 1;
return fib.memoized(n-1) + fib.memoized(n-2);
}
Here we can see that the memoized
method is applied on the fib
function, i.e. your this
keyword refers to the fib
function. It does not relaunch the memoized
function, but "launches" the function on which it was called. However, it does call it with this
set to the function itself, which does not make any sense. Better:
Function.prototype.memoized = function(key){
if (!this._values)
this._values = {};
if (key in this._values)
return this._values[key];
else
return this._values[key] = this.apply(null, arguments);
// pass null here: ^^^^
}
Even better would be if memoized
would return a closure:
Function.prototype.memoized = function(v) {
var fn = this, // the function on which "memoized" was called
values = v || {};
return function(key) {
if (key in values)
return values[key];
else
return values[key] = fn.apply(this, arguments);
}
}
var fib = function(n) {
if (n < 2) return 1;
return fib(n-1) + fib(n-2);
}.memoized();
// or even
var fib = function(n) { return fib(n-1) + fib(n-2) }.memoized({0:1, 1:1});