How to add a space every three characters from the right of a string in Javascript?

Question

I can do it with this:

const mystring = 'abcdefgh' // or '00000000'
mystring.replace(/(.{3})/g, '$1 ')

But then I get abc def gh.

How to do it from the right and get ab cde fgh ?

Answer 1

Lookahead for groups of 3 characters, eventually followed by the end of the string:

const mystring = '00000000'
console.log(
  mystring.replace(/(?=(?:.{3})*$)/g, ' ')
);