function beforeAt(email) {
  var alphabet = [
    "a","b","c","d","e",
    "f","g","h","i","j",
    "k","l","m","n","o",
    "p","q","r","s","t",
    "u","v","w","x","y",
    "z"
  ];

  var numbers = [ "1","2","3","4","5","6","7","8","9","0" ];

  var legalChar = ["a","b","c","d","e",
  "f","g","h","i","j",
  "k","l","m","n","o",
  "p","q","r","s","t",
  "u","v","w","x","y",
  "z", "1","2","3","4",
  "5","6","7","8","9","0",
  "_", "."]; // these are the only legal characters before @ symbol

  var addressArray = email.split("@");
  if(addressArray.length > 2){ // if there are more than 2 splits, then return false
    return false;
  } else {
    for (var i = 0; i < addressArray[0].length; i++){// start at split 0, ie. before the @
      var beforeAt = addressArray[0].length[i]; // declaring before @
      if((legalChar.indexOf(beforeAt)) !== -1){ // return true if only legal characters exist
        return true;
      }
    }
  }
  return false;
}

console.log("mlbpro417@gmail.com");
console.log(beforeAt("mlbpro417@gmail.com"));
console.log("mlbpro417!@gmail.com");
console.log(beforeAt("mlbpro417!@gmail.com"));