Array Prototype Last

LeetCode #2619 🟢 Easy JavaScript Solve by @noeyislearning

Problem Statement

Write code that enhances all arrays such that you can call the array.last() method on any array and it will return the last element. If there are no elements in the array, it should return -1.

You may assume the array is the output of JSON.parse.

Example 1:

Input: nums = [null, {}, 3]
Output: 3
Explanation: Calling nums.last() should return the last element: 3.

Example 2:

Input: nums = []
Output: -1
Explanation: Because there are no elements, return -1.

Constraints:

• arr is a valid JSON array
• 0 <= arr.length <= 1000

Solution

Array.prototype.last = function () {
  return this.length > 0 ? this[this.length - 1] : -1
}

Explanation

Think of arrays like boxes full of stuff. You can have boxes with toys, snacks, or maybe even an empty box! Normally, if you want to know what's at the very end of the box, you have to dig through it all. This code is like giving all your boxes a superpower!

This code is like a tiny instruction you teach all your boxes:

1. ("My Name is Last") Every box now has the ability to tell you what it calls the ".last()" thing. Imagine it's a special code word.

2. (Check If Full) First, the box peeks inside (this.length > 0). Is there anything in there?

   • If yes: It quickly jumps to the very back (this[this.length - 1]) and tells you what it finds.
   • If no: It gives you a "-1" signal, which means the box was empty.

More Examples

Example 1 — nums has [null, {}, 3] @noeyislearning

• You ask, "nums, what's your .last()?"
• It checks… not empty!
• It jumps to the back and says, "I found a 3!"

Example 2 — nums is empty [] @noeyislearning

• You ask, "nums, what's your .last()?"
• It checks... nothing inside.
• It gives you the signal "-1".