Validating alphabetic only string in javascript

Question

How can I quickly validate if a string is alphabetic only, e.g

var str = "!";
alert(isLetter(str)); // false

var str = "a";
alert(isLetter(str)); // true

Edit : I would like to add parenthesis i.e () to an exception, so

var str = "(";

or

var str = ")";

should also return true.

Answer 1

Regular expression to require at least one letter, or paren, and only allow letters and paren:

function isAlphaOrParen(str) {
  return /^[a-zA-Z()]+$/.test(str);
}

Modify the regexp as needed:

• /^[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