How to force input to only allow Alpha Letters?

Question

using jQuery here, however unable to prevent numbers from being typed into the input field

http://codepen.io/leongaban/pen/owbjg

Input

Answer 1

function alphaOnly(event) {
  var key = event.keyCode;`enter code here`
  return ((key >= 65 && key <= 90) || key == 8);
};