class Stack {

constructor(length) {

this._items = new Array(length);

this._index = 0;

}

get length() {

return this._index;

}

get isEmpty() {

return this._index === 0;

}

get isFull() {

return this._index === this._items.length;

}

peek() {

if (this.isEmpty) {

throw new RangeError("Cannot peek at an empty stack!");

}

return this._items[this._index - 1];

}

pop() {

if (this.isEmpty) {

throw new RangeError("Cannot pop from an empty stack!");

}

this._index -= 1;

const item = this._items[this._index];

this._items[this._index] = undefined;

return item;

}

push(item) {

if (this.isFull) {

throw new RangeError("Cannot push into a full stack!");

}

this._items[this._index] = item;

this._index += 1;

}

}

module.exports = Stack;