Array.prototype.inCommon = function(arr2) {
	const arr1 = this;
	if (arr2.length > arr1.length) {
		return arr1.filter(i => {
			return arr2.indexOf(i) > -1;
		});
	} else {
		return arr2.filter(i => {
			return arr1.indexOf(i) > -1;
		});
	}
};