ES5 Array methods as applied to Object.prototype (map and filter are currently incorrect implementations)

object.prototype-array-methods.js

// ES5 Array methods
// New methods added: Array.isArray, indexOf, lastIndexOf, every, some,
// forEach, map, filter, reduce, reduceRight
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

// Array.prototype.reduce(function (previousValue, currentValue, currentIndex, array), initialValue)
if (!Object.prototype.reduce) {
	Object.prototype.reduce = function (callback, initialValue) {
		var _this = this;
		return Object.keys(_this).reduce(function (acc, key, i) {
			return callback(acc, _this[key], key, _this);
		}, initialValue);
	};
}

// Array.prototype.forEach(function (currentValue, index, array), thisArg)
if (!Object.prototype.forEach) {
	Object.prototype.forEach = function (callback, thisBinding) {
		var _this = this;
		Object.keys(_this).forEach(function (key, i) {
			callback.apply(thisBinding, [_this[key], key, _this]);
		});
		return undefined;
	};
}

// Array.prototype.map(function (currentValue, index, array), thisArg)
if (!Object.prototype.map) {
	Object.prototype.map = function (callback, thisBinding) {
		var _this = this;
		return Object.keys(_this).map(function (key, i) {
			return callback.apply(thisBinding, [_this[key], key, _this]);
		});
	}
}

// Array.prototype.filter(function (currentValue, index, array), thisArg)
if (!Object.prototype.filter) {
	Object.prototype.filter = function (callback, thisBinding) {
		var _this = this;
		return Object.keys(_this).filter(function (key, i) {
			return callback.apply(thisBinding, [_this[key], key, _this]);
		});
	}
}