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();