declare global {
	interface Array<T> {
		/** @summary check if any of the elements of `arr2` are included in `this` */
		anyOf(arr2: Array<T>): boolean;
		/** @summary return last element of array without removing it */
		peek(): T;
		/** @summary create Set from this array */
		set(): Set<T>;
		/** @summary clear array */
		clear(): void;
	}
}

Array.prototype.anyOf = function(arr2) {
	return !!this.filter(e => arr2.includes(e)).length;
};

Array.prototype.peek = function() {
	return this[this.length - 1];
};

Array.prototype.set = function() {
	return new Set(this);
}

Array.prototype.clear = function() {
	while (this.length > 0) this.pop();
}