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

When you place a pattern inside a capturing group, split will return the matched delimiters as even array items. So, all you need to do is modify the odd items:

var counter=1;
var str = "Hello+Beautiful#World";
console.log(
  str.split(/([+#])/).map(function(el, index){
    return el + (index % 2 === 0 ? (counter++ + "").padStart(3, '0') : '');
  }).join("")
);