Find and replace nth occurrence of [bracketed] expression in string

Question

I have a form where the name attributes get updated, but the problem is im using multidimensional values as follows:

Answer 1

The approach given in the accepted answer is concise and solid, but it has a drawback: if there's a big string with a lot of appearances of the given substring, it will be scanned till the end - even if one has to replace only at the beginning. The alternative would be using 'exec', then breaking off the chain right after the replacement is done:

function replaceNthOccurence(source, pattern, replacement, n) {
  var substr = '';
  while (substr = pattern.exec(source)) {
    if (--n === 0) {
      source = source.slice(0, substr.index) + replacement + source.slice(pattern.lastIndex);
      break;
    }
  }
  return source;
}

console.log( replaceNthOccurence('bla_111_bla_222_bla_333', /\d+/g, '1st', 1) );
console.log( replaceNthOccurence('bla_111_bla_222_bla_333', /\d+/g, '2nd', 2) );
console.log( replaceNthOccurence('bla_111_bla_222_bla_333', /\d+/g, '3rd', 3) );