Stack.js

class Stack {
    constructor() {
        this.items = [];
        this.top = null;
    }

    getTop() {
        if (this.items.length == 0)
            return null;
        return this.top;
    }

    isEmpty() {
        return this.items.length == 0;
    }

    size() {
        return this.items.length;
    }

    push(element) {
        this.items.push(element);
        this.top = element;
    }

    pop() {
        if (this.items.length != 0) {
            if (this.items.length == 1) {
                this.top = null;
                return this.items.pop();
            } else {
                this.top = this.items[this.items.length - 2];
                return this.items.pop();
            }

        } else
            return null;
    }


}

var myStack = new Stack();

for (var i = 0; i < 5; i++) {
    myStack.push(i);
}

console.log("Is stack empty? " + myStack.isEmpty());
console.log("top: " + myStack.getTop());

for (var i = 0; i < 5; i++) {
    console.log("Element popped: " + myStack.pop());
    console.log("top: " + myStack.getTop());
}

console.log("Is stack empty?: " + myStack.isEmpty());
console.log("top: " + myStack.getTop());