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

    id="name"
    name="name"
    class="form-control verify-input"
    type="text"
    ng-model="volume.name"
    ng-maxlength="255"
    ng-disabled="context.mode === 'extend' ||
                 context.mode === 'attach' ||
                 context.mode === 'detach'"
    placeholder="{% trans 'enter a volume name' %}"/>
  <p class="help-block alert-fixed alert-danger"
    ng-show="form.name.$error.required && form.name.$dirty">
    {% trans "A volume name is required." %}
  </p>
  <p class="help-block alert-fixed alert-danger"
    ng-show="form.name.$error.maxlength && form.name.$dirty">
    {% trans "Name length should be less than 255 chars." %}
  </p>
  <p class="help-block alert-fixed alert-danger"
    ng-show="form.name.$error.validateNumberLetter && form.name.$dirty">
    {% trans "should be letter" %}
  </p>
</div>