Stack_Array

class Node {
    constructor(value) {
        this.value = value;
        this.next = null;
    }
}

class Stack {
    constructor() {
        this.arr = [];
    }
    
    peek() {
        return this.arr[this.arr.length-1];
    }
    
    push(value) {
        this.arr.push(value);
        return this;
    }
    
    pop() {
        if (this.arr.length === 0) {
            return null;
        }
        
        if (this.arr.length === 1) {
            return this.arr.pop();
        }
        
        this.top = this.arr[this.arr.length-1];
        return this.arr.pop();
    }
    
    isEmpty() {
        return (this.length === 0);
        
    }
    
    // print the elements in the stack
    printList() {
        console.log(this.arr.join(" | "));
    }
}

const myStack = new Stack();
console.log(myStack.isEmpty());
myStack.push(10);
myStack.push(20);
myStack.push(30);
myStack.push(40);
console.log(myStack.peek());
myStack.printList();
console.log(myStack.pop());
myStack.printList();
console.log(myStack.pop());
myStack.printList();
console.log(myStack.isEmpty());
console.log(myStack.length);
console.log(myStack);