helpful array methods- empty and contains, and property last

array_methods.js

Object.defineProperty(Array.prototype, 'last', {
    enumerable: false,
    configurable: true,
    get: function() {
        return this[this.length - 1];
    },
    set: undefined
});

/**
 * check whether array contains supplied item
 */
Object.defineProperty(Array.prototype, 'contains', {
    enumerable: false,
    configurable: false,
	/**
	 * @param {*} val
	 * @returns {boolean}
	 */
    value: function (val) {
        return this.indexOf(val) != -1;
    },
    writable: false
});

/**
 * will erase the array and leave it empty
 */
Object.defineProperty(Array.prototype, 'empty', {
    enumerable: false,
    configurable: false,
    value: function () {
        this.length = 0;
    },
    writable: false
});