with stuff

function LetterCapitalize(str) {   // str = "this is test"
  return str.split(' ') // ["this", "is", "test"]
    .map(function(word){
    return word[0].toUpperCase() + word.substring(1); //  ["This", "Is", "Test"]
    })
    .join(' '); //  "This Is Test"
}