JavaScript Data Structures - Stack

Definition

A stack is a linear data structure that behaves like a real-world stack of items. It follows a last in, first out (LIFO) order of operations, similar to its real-world counterpart. This means that new items are added to the top of the stack and items are removed from the top of the stack as well.

The main operations of a stack data structure are:

• push: Adds an element to the top of the stack
• pop: Removes an element from the top of the stack
• peek: Retrieves the element at the top of the stack, without removing it
• isEmpty: Checks if the stack is empty

Implementation

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

  push(item) {
    this.items.unshift(item);
  }

  pop(item) {
    return this.items.shift();
  }

  peek(item) {
    return this.items[0];
  }

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

• Create a class with a constructor that initializes an empty array, items, for each instance.
• Define a push() method, which uses Array.prototype.unshift() to add an element to the start of the items array.
• Define a pop() method, which uses Array.prototype.shift() to remove an element from the start of the items array.
• Define a peek() method, which retrieves the value of the first element in the items array, without removing it.
• Define an isEmpty() method, which uses Array.prototype.length to determine if the items array is empty.

const stack = new Stack();

stack.push('apples');
stack.push('oranges');
stack.push('pears');

stack.isEmpty();    // false

stack.peek();       // 'pears'

stack.pop();        // 'pears'
stack.pop();        // 'oranges'
stack.pop();        // 'apples'

stack.isEmpty();    // true