What are JavaScript arrays and their methods?

Arrays are ordered collections of elements in JavaScript.

Creating Arrays:

const arr1 = [1, 2, 3];
const arr2 = new Array(1, 2, 3);

Common Methods:

Mutating methods:
- push() - add to end
- pop() - remove from end
- shift() - remove from start
- unshift() - add to start
- splice() - add/remove elements
- sort() - sort elements
- reverse() - reverse order

Non-mutating methods:
- concat() - join arrays
- slice() - extract portion
- indexOf() - find index
- includes() - check existence

Iteration methods:
- forEach() - execute function for each
- map() - transform elements
- filter() - filter elements
- reduce() - reduce to single value
- find() - find first match
- some() - test if any match
- every() - test if all match