Stack Peek

Peek Operation

Returns the topmost element from the stack without removing it.

Example: Peeking at a stack

  1. Current stack: [7, 3, 5]
  2. Peek → returns 7: [7, 3, 5] (stack remains unchanged)
  3. After pop: [3, 5]
  4. Peek → returns 3: [3, 5]
  • Time Complexity: O(1)
  • Space Complexity: O(1)

The peek operation is useful when you need to inspect the top element before deciding whether to pop it or push another element onto the stack.

Visualize Push, Pop, and Peek operations

Stack Visualization

Stack is empty
Stack is empty
Top
Current top
Peek
Viewing
Elements
Stack items

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Stack Push & Pop Implementation

// Stack Implementation with Peek Operation in JavaScript
class Stack {
  constructor() {
    this.items = [];
    this.top = -1;
  }

  // Push operation
  push(element) {
    this.items[++this.top] = element;
    console.log(`Pushed: ${element}`);
  }

  // Pop operation
  pop() {
    if (this.isEmpty()) {
      console.log("Stack Underflow");
      return -1;
    }
    return this.items[this.top--];
  }

  // Peek operation
  peek() {
    if (this.isEmpty()) {
      console.log("Stack is empty");
      return -1;
    }
    console.log(`Top element: ${this.items[this.top]}`);
    return this.items[this.top];
  }

  // Check if stack is empty
  isEmpty() {
    return this.top === -1;
  }

  // Display stack
  display() {
    console.log("Current Stack:", this.items.slice(0, this.top + 1));
  }
}

// Usage
const stack = new Stack();
stack.push(10);
stack.push(20);
stack.push(30);
stack.display();
stack.peek();
stack.pop();
stack.peek();

Explore other operations

Push & Pop

Is Empty

Is Full