Flatten an array

This function flattens an array, meaning it removes one level of nesting.

JavaScript:

let flatten = arr => arr.flat();

// Example
console.log(flatten([[1, 2], [3, 4], [5, 6]])); // [1, 2, 3, 4, 5, 6]
console.log(flatten([['a', 'b'], ['c', 'd'], ['e', 'f']])); // ['a', 'b', 'c', 'd', 'e', 'f']

TypeScript:

let flatten = (arr: T[][]): T[] => arr.flat();

// Example
console.log(flatten([[1, 2], [3, 4], [5, 6]])); // [1, 2, 3, 4, 5, 6]
console.log(flatten([['a', 'b'], ['c', 'd'], ['e', 'f']])); // ['a', 'b', 'c', 'd', 'e', 'f']