allUnique.js

/*

From Cassidy Williams' weekly newsletter (https://click.pstmrk.it/2sm/buttondown.email%2Fcassidoo%2Fsubscribers%2F4d5ba807-3668-4d77-9db5-4e3303c0f3a9%2Farchive%2Fkeep-your-face-always-toward-the-sunshine-and/WPtx8C0N/bP1H/IfMBgFIdr5/OGIyZDRjMjctMTAzMy00Y2Y2LWI2YWMtZjVlNTRiOWFmNDA1)

Write a function that determines if all the characters in a given string are unique. Can you do this without making any new variables? You choose if you want to include capitalization in your consideration for this one, as a fun challenge.

Example: 

> allUnique('Cassidy')
> false

> allUnique('cat & dog')
> false

> allUnique('cat+dog')
> true

*/

export const allUnique = (chars, ignoreCase) => !RegExp(/([\s\S])[\s\S]*(?=\1)/, ignoreCase ? ['i'] : []).test(chars);