Join the string with same separator used to split

Question

I have a string that need to be split with a regular expression for applying some modifications.

eg:

const str = \"Hello+Beautiful#World\";
const spl         


        

Answer 1

Don't use split and join in this case. Use String.replace(), and return the modified strings:

const str = "Hello+Beautiful#World";

let counter = 1;
const result = str.replace(/[^\+#]+/g, m =>
  `${m.trim()}${String(counter++).padStart(3, '0')}`
);

console.log(result);

Another option, which might not fit all cases, is to split before the special characters using a lookahead, map the items, and join with an empty string:

const str = "Hello+Beautiful#World";

let counter = 1;
const result = str.split(/(?=[+#])/)
  .map(s => `${s.trim()}${String(counter++).padStart(3, '0')}`)
  .join('')

console.log(result);