[JS][Func] Replace word in sentence w/ preserved capitals

function replaceWord(str, before, after)
{
  var re = new RegExp(before, 'gi');
  after = (before[0].toUpperCase() == before[0] ? after = after[0].toUpperCase() + after.slice(1) : after);//if first letter of before is capitalized, it'll change after to capitalized as well.
  str = str.replace(re, after);
  return str;
}