Stack (Array)

class Stack {
    constructor() {
        this.elements = [];
        this.length = 0;
    }
    
    push(value) {
        this.elements.push(value);
        this.length++;
    }
    
    peek() {
        return this.elements[this.length - 1];
    }
    
    pop() {
        if(this.length === 0) {
            return null;
        }
        this.length--;
        return this.elements.pop();
    }
    
    isEmpty() {
        return (this.length === 0) ? true : false;
    }
}

const stack = new Stack();
stack.push(1);
stack.push(2);
stack.push(3);
console.log(stack);
console.log(stack.pop());
console.log(stack.pop());
console.log(stack.peek());
console.log(stack.isEmpty());
console.log(stack.pop());
console.log(stack.isEmpty());
console.log(stack);
console.log(stack.pop());