[Javascript] - Power of two memozing function with closure

memozing-function.js

Function.prototype.memoized = function(key) {
    this._values = this._values || {};
    return this._values[key] !== undefined ?
        this._values[key] :
        this._values[key] = this.apply(this, arguments);
}

Function.prototype.memoize = function() {
    var fn = this;
    return function() {
        fn.memoized.apply(fn, arguments);
    }
}

var isPowerOfTwo = (function(n) {
    return !(n & (n - 1)); // binary operator
}).memoize();