# Arrays - The Must Have

> Practice and refresh the most essential array methods in JavaScript — from map, filter, and reduce to powerful combinations that make data handling in React effortless.

- Difficulty: beginner
- Estimated time: 30 minutes
- Tests: 12
- Requires subscription: yes

## Overview

Practice and refresh the most essential array methods in JavaScript — from map, filter, and reduce to powerful combinations that make data handling in React effortless.


## Requirements

- Use only built-in JavaScript array methods (`map`, `filter`, `find`, `some`, `every`, `reduce`, `sort`, etc.).
- Avoid using traditional `for` or `while` loops.
- Return new arrays or values instead of mutating the original data.
- Chain multiple methods when necessary to achieve more complex transformations.
- Make sure to handle possible `null` or `undefined` values safely (e.g., using optional chaining or default values).


## Notes

- Each test focuses on a core array method you’ll commonly use when working with data in React components.
- Pay attention to methods that **return arrays** (`map`, `filter`, `sort`) versus those that **return a single value** (`find`, `some`, `every`, `reduce`).
- When sorting or reducing, ensure numeric operations handle missing ages or invalid data gracefully.
- Revisit this challenge periodically — mastering these operations is key to writing concise, expressive React logic.


## Tests

01. returns array with name and gender
02. filters deceased characters
03. finds character named 'Lisa'
04. filters adult male characters and maps basic info
05. maps alive character names
06. returns total number of characters
07. checks if any character is under 18
08. checks if all characters have gender
09. sorts characters by ascending age
10. sorts character names alphabetically
11. calculates average age of alive characters as number with one decimal
12. returns phrases that contains the word 'no' (case insensitive) with character name