angular js input校验只能输入数字和字母 directive写法一则

js代码:
.directive('validateNumberLetter', function () {
  return {
    require: 'ngModel',
    link:    function (scope, elm, attrs, ctrl) {
      scope.$watch(attrs.ngModel, function(n){
        if(!n) return;
        var oldName = attrs.validateNumberLetter;
        if(oldName !== n){
          var reg=/[^A-Za-z0-9]/;
          if (n.length) {
            if(reg.test(n)){
              // it is invalid, return undefined (no model update)
              ctrl.$setValidity('validateNumberLetter', false);
              return undefined;
            }else{
               // it is valid
              ctrl.$setValidity('validateNumberLetter', true);
              return n;
            }
          }
        }
      });
    }
  };
})
html代码:

<div class="form-group-right">
  <input required validate-number-letter

     %}
  </p>
</div>