function Stack() {    var items = [];    this.push = function(element){        items.push(element);    }    this.pop = function(){        return items.pop();    }    this.peek = function() {        return items[items.length -1];    }    this.isEmpty = function() {        return items.length == 0;    }    this.size = function() {        return items.length;    }    this.clear = function(){        items = [];    }    this.print = function() {        console.log(items.toString());    }}var stack = new Stack();console.log(stack.isEmpty());stack.push(5);stack.push(8);console.log(stack.peek());stack.push(11);console.log(stack.size());console.log(stack.isEmpty());stack.push(15);stack.pop();stack.pop();console.log(stack.size());stack.print();