JavaScript Program to Implement a Stack Using an Array

A stack is a Last-In-First-Out (LIFO) data structure — the last element added is the first one removed, like a stack of plates. JavaScript arrays already behave like a stack if you only use push() and pop(), but wrapping that behavior in a class makes the intent explicit and prevents accidental misuse of other array methods.

JavaScript Program to Implement a Stack Using an Array

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

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

  pop() {
    if (this.isEmpty()) return "Stack is empty";
    return this.items.pop();
  }

  peek() {
    if (this.isEmpty()) return "Stack is empty";
    return this.items[this.items.length - 1];
  }

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

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

const stack = new Stack();
stack.push(10);
stack.push(20);
stack.push(30);

console.log("Top element:", stack.peek());
console.log("Popped:", stack.pop());
console.log("Stack size after pop:", stack.size());

Output:

Top element: 30
Popped: 30
Stack size after pop: 2

All four operations — push, pop, peek, and isEmpty — run in O(1) constant time because they only ever touch the end of the underlying array, never shift or re-index the rest of it. Stacks like this show up constantly in real code: the browser’s back-button history, the call stack behind function execution and recursion, undo/redo features, and balanced-parentheses/bracket-matching checks.