Intersperse element between elements

JavaScript

const intersperse = (a, s) => [...Array(2 * a.length - 1)].map((_, i) => (i % 2 ? s : a[i / 2]))

TypeScript

const intersperse = <T>(a: T[], s: T): T[] => [...Array(2 * a.length - 1)].map((_, i) => (i % 2 ? s : a[i / 2]))

Examples

intersperse(['A', 'B', 'C'], '/') // ['A', '/', 'B', '/', 'C']
intersperse([<li>A</li>, <li>B</li>, <li>C</li>], <li>/</li>) // [<li>A</li>, <li>/</li>, <li>B</li>, <li>/</li>, <li>C</li>]