is-array.js

// D. Crockford's method for adding methods to the prototype object
Function.prototype.method = function (name, func) {
	this.prototype[name] = func;
	return this;
};

// Add is_array function to Array, return true
Array.method('is_array', function () {
	return true;
});

// Add is_array function to Object, return false
Object.method('is_array', function () {
	return false;
});

var collection_1 = {}; // Object, should return undefined
var collection_2 = []; // Array, should return true

// Return some intuitive text for testing
var test_array = function (collection) {
	return collection.is_array() ? 'Totally an array.' : 'Definitely not an array, man.';
};

document.writeln(test_array(collection_1)); // Definitely not an array, man.
document.writeln(test_array(collection_2)); // Totally an array.

Javascript doesn't come with a native is_array function. The solutions I've seen have seemed unnecessarily complex. I've been wondering why this particular solution wouldn't work?