gistfile1.js

// run here (use the data-uri below as an address):
// data:text/html;ascii,<script src="https://gist.github.com/raw/4427971/cef83fed8b6de8bfbb9fa3ae461b724fff87c057/gistfile1.js" type="text/javascript"></script>

// The technique used here is based on an article by Ashley Gullen: http://netm.ag/SWI0E5

// Array#slice returns an array with the seleted range of items.
// Because a new array is created every time you use this method, however,
//    all these arrays are in memory, which means the JavaScript GC (Garbage Collection)
//    has to collect up all of these unused arrays and throw them away.
// In performance-critical situations, such as in a game-loop that needs to run within 
//    16ms (60 frames times per second), GC can really mess with your smooth animations and such.
// To stop slicing from creating new arrays each time, you can mutate the array itself instead.
Array.prototype.slice_mutate = function slice_mutate(from, to) {
	// first we set the array's length to the item at the "to" position
	this.length = to;
	// any items that were after the "to" position will be discarded
	
	// from the first item...
	i = 0;
	// ...loop through all items before the "from" position...
	while (from--) {
		// ...removing each item as we go
		this.shift();
	}
	
	// we have now removed all items before the "from" position
	//    and after the "to" position
	// and so the array now contains a slice of items between positions
	//    "from" and "to".
	
	return this;
};


// console shim
(function () {
	if (!window.console) { window.console = {}; }

	var c = window.console;
	if (!c.log) { c.log = function () { }; }
	if (!c.group) { c.group = function (label) { c.log("__" + label + "__"); }; }
	if (!c.groupEnd) { c.groupEnd = function () { }; }
})();

// tests
var a = ["a", "b", "c", "d"];
console.group("a.slice(1,3)");
console.log("a: ", a);
console.log("returns: ", a.slice(1, 3));
console.log("after: ", a);
console.groupEnd();

var b = ["a", "b", "c", "d"];
console.group("b.slice_mutate(1,3)");
console.log("returns: ", b.slice_mutate(1, 3));
console.log("after: ", b);
console.groupEnd();