Using $index with the AngularJS 'ng-options' directive?

Since arrays are very similar to objects in JavaScript, you can use the syntax for "object data sources". The trick is in the brackets in the ng-options part:

var choices = [
  'One',
  'Two',
  'Three'
];

In the template:

<select
  ng-model="model.choice"
  ng-options="idx as choice for (idx, choice) in choices">
</select>

In the end, model.choice will have the value 0, 1, or 2. When it's 0, you will see One; 1 will display Two, etc. But in the model, you will see the index value only.

I adapted this information from "Mastering Web Application Development with AngularJS" by PACKT Publishing, and verified at the Angular reference documentation for select.

Since you can't use $index but you can try indexOf.

HTML

<div ng-app ng-controller="MyCtrl">
    <select 
          ng-model="selectedItem"
          ng-options="values.indexOf(selectedItem) as selectedItem for selectedItem in values"></select>
    selectedItem: {{selectedItem}}
</div>

Controller

function MyCtrl($scope) {
    $scope.values = ["Value1","Value2"];
    $scope.selectedItem = 0;
}

Demo Fiddle

Comment:

Array.prototype.indexOf is not supported in IE7 (8)

$index is defined for ng-repeat, not select. I think this explains the undefined. (So, no, this shouldn't work.)

Angular supports binding on the entire object. The documentation could be worded better to indicate this, but it does hint at it: "ngOptions ... should be used instead of ngRepeat when you want the select model to be bound to a non-string value."

You can also use ng-value='$index' in <option> tag.

<select ng-model="selData">
 <option ng-repeat="d in data track by $index" ng-value="$index">
   {{d.name}}
 </option>
</select>