how to check if a string is alphabetic in javascript

function isLetter(str) {
  return str.length === 1 && str.match(/[a-z]/i);
}function isAlphaOrParen(str) {
  return /^[a-zA-Z()]+$/.test(str);
}

/*/^[a-zA-Z()]*$/ - also returns true for an empty string
/^[a-zA-Z()]$/ - only returns true for single characters.
/^[a-zA-Z() ]+$/ - also allows spaces*/
//better regEX to include question marks too