function myReplace(str, before, after) {

  //return str;

  if(before[0] === before[0].toUpperCase()){

    after = after[0].toUpperCase() + after.slice(1);

  }

  str = str.replace(before,after);

  return str;

}

myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");

function myReplace(str, before, after) {

  //return str;

  var re = /^[A-Z]/;

  if(re.test(before.charAt(0))){

    after = after.charAt(0).toUpperCase() + after.slice(1);

  }

  str = str.replace(before,after);

  return str;

}

myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");