jQuery Form Field Jumper Plugin

/* jquery.fieldjump.js */

jQuery.fn.jumpsTo = function(element) {
  this.bind('keyup', {to: element}, function(event) {
    var to = $(event.data.to)
    var from = $(event.target)

    var keys_typed = from.val().length;
    var keys_required = from.attr('maxlength');

    if (isNumber(event.keyCode) && keys_typed == keys_required)
    {
      to.focus();
      if (to[0].type == 'text') {
        to.val('');
      }
    }
  });

  return this;
}

function isNumber(n) {
  return (n >= 48 && n <= 57) || (n >= 96 && n <= 105);
}