Edit in JSFiddle

function siblings(){
  var siblings =["John", "Liza", "Peter"];
  function siblingCount(){
    var siblingsLength = siblings.length;
    return siblingsLength;
  }

  function joinSiblingNames(){
    return "I have " + siblingCount() + " siblings:\n\n" + siblings.join("\n");
  }
  return joinSiblingNames();
}

alert(siblings()); //輸出 "I have 3 siblings: John Liza Peter"