Using Objects for Lookups
function phoneticLookup(val) {
  var result = "";
  var lookup = {
     "alpha":"Adams",
     "bravo":"Boston",
     "charlie":"Chicago",
     "delta":"Denver",
     "echo":"Easy",
     "foxtrot":"Frank",
  };
  result = lookup[val];
  return result;
}
phoneticLookup("charlie");
console.log(phoneticLookup("alpha")); // to test
console.log(phoneticLookup("")); //to test