Read the Final Value of an Array
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Extend JavaScript arrays with a method named `last`, so that calling `items.last()` returns the final element of `items`. If the array is empty, return the number `-1`.
Implement `Array.prototype.last`. It takes no arguments; the array receiving the method call supplies the elements. Return the final value unchanged, including when it is `null`, `false`, `0` or an empty string. Reading the final element must not remove or replace array elements.
### Examples
**Example 1:**
```javascript
const items = JSON.parse('[8, "done", false]');
items.last(); // false
```
The final value is `false`; the array is not empty.
**Example 2:**
```javascript
const items = JSON.parse('[{"ready": true}, null]');
items.last(); // null
```
The final value is `null`, so that exact value is returned. An empty array would instead return `-1`.
### Constraints
- Each receiver is an array produced by `JSON.parse` from valid JSON array text.
- `0 <= items.length <= 1000`.
- Elements may be JSON nulls, booleans, numbers, strings, arrays or objects. Nested JSON values are allowed.
- The task does not require handling sparse arrays, `undefined` elements or non-array receivers.
### What a Strong Answer Covers
- Make `last()` available through the required array method contract.
- Distinguish an empty array from a nonempty array with a falsy final value.
- Preserve array contents and return object or array elements themselves, without making copies.
### Follow-up Questions
- If the final value is an object, what relationship should hold between the returned object and that array element?
- If the final value is the number `-1`, can the return value alone distinguish that array from an empty one?
Overview: Add a JavaScript array method that returns the final value unchanged, preserving null and falsy elements and handling empty arrays.