Javascript cache wrapping

caching_wrapper.js

var $w = function(string) { return string.split(' '); };

var asInts = function(arr) { 
	var results=[]; 
	for(var i=0, m=arr.length; i<m; i++) results.push(parseInt(arr[i], 10));
	return results;
};

Array.prototype.map = function(func) { 
	var results=[]; 
	for(i=0, m=this.length; i<m; i++) results.push(func(this[i])); 
	return results; 
};

var time = function(subject, label) { 
	this.seq = 1; 
	var name = label || this.seq++; 
	console.time(name); 
	subject(); 
	console.timeEnd(name); 
} 

var primes = asInts($w('524287 9369319 2147483647'));
var notprimes = asInts($w('4 6 8 15 21 524284 9369312'));

function isPrime(num) {
	if (!num) return false;
	var prime = num != 1;
	 for ( var i = 2; i < num; i++ ) { 
	   if ( num % i == 0 ) { 
	     prime = false; 
	     break; 
	   } 
	 }
	return prime;
}

Function.prototype.cached = function() {
	var self = this;
	if (!self.cache) self.cache = {};
	
	return function(o) {
		if (self.cache[o] == null) {
			console.log('cache miss');
			self.cache[o] = self(o);
		} else { console.log('cache hit'); }
		return self.cache[o];
	}	
};

isPrimeCached = isPrime.cached();


time(function(){ primes.map(isPrime); }, 'isprime-no-cache');
time(function(){ primes.map(isPrimeCached); }, 'isprime-with-cache first');
time(function(){ primes.map(isPrimeCached); }, 'isprime-with-cache repeated');