Peek Operation in Stacks and Arrays in JavaScript

Published October 7, 2020

The peek() method is used to only view the last element of an array or view the recently added element in a stack data structure.

Unfortunately, there is no method called peek() in the Array object. We have to implement it ourselves in JavaScript.

All we have to do is get the last element but do not remove it.

It can be done like this,

const lastElement = array[array.length - 1];

But if you want to add this as a method to the Array object, you have to add this as a method to the Array prototype chain.

So let's add our peek() method to the Array prototype chain,

// Adding peek method to the Array
// prototype chain
Array.prototype.peek = function () {
  if (this.length === 0) {
    throw new Error("out of bounds");
  }
  return this[this.length - 1];
};

The function first checks whether the length of the array is 0, If it is true then it will make an Error, if its false then it will return the last element.

Now you can use the peek() method just like how you would use the push(), pop() array methods.

// Adding peek method to the Array
// prototype chain
Array.prototype.peek = function () {
  if (this.length === 0) {
    throw new Error("out of bounds");
  }
  return this[this.length - 1];
};

// array
const arr = [1, 2, 3, 4, 5, 6];

// peek() method
const element = arr.peek();
console.log(element); // 6

See this example live in JSBin.

Feel free to share if you found this useful 😃.


Share on: Facebook Twitter