What is causing the issue of blank options not being configured for ng-options inside a directive?

I am currently working on developing an AngularJS Directive for handling the prompts of a <select> input. There are 3 different modes that I am implementing:

  1. Disallowing a blank option
    • This is the default mode
  2. Allowing a blank option with no text
    • This can be achieved by setting allow-blank="true" within the directive
  3. Allowing a blank option with prompt text
    • This can be achieved by setting allow-blank to any value other than "true"

However, it seems that the blank options are not appearing.

Check out the demo on Plunker

Template

<select ng-options="tag.id as tag.name for tag in myTags">
  <option ng-if="allowBlank === 'true'" value=""></option>
  <option ng-if="allowBlank && allowBlank !== 'true'" value="">{{allowBlank}}</option>
</select>

Directive

myApp.directive('mySelector', ['$http', function($http) {
  return {
    templateUrl:'my-selector-template.html',
    restrict: 'E',
    scope: {
      allowBlank: '@?'
    },
    replace: true,
    controller: function ($scope) {
      $scope.myTags = [
        {"name":"aliquam in","id":1},
        {"name":"massa velit","id":2},
        {"name":"nec vestibulum","id":3}
      ];
    }
  };
}]);

Answer №1

One issue is that the select content is not directly included (see below). The option tags defined inside are not visible when inspecting the output elements.

If you are simply using a string, it's recommended to utilize a pre-linking function to dynamically add the correct options using JavaScript. The code snippet below can help accomplish this (Derived from this Plunk).

link: {
  pre: function(scope, element, attrs){
    if(attrs.allowBlank === 'true') element.append('<option value=""></option>');
    else if(attrs.allowBlank && attrs.allowBlank !== '') element.append('<option value="">' + attrs.allowBlank + '</option>');
  }
}

UPDATE: The select does not actually 'transclude' its contents. As @lightswitch05 mentioned, the select directive fetches the first child with value="" as the empty node (source reference). It then clears out the select's contents and dynamically inserts the appropriate <option> tags later on (source reference)

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