Angular issue: There is a different this (inside the method - different scope object), if controller method is defined in instance than if defined in prototype. This applies only when related element has been created by ng:repeater.

angular-controller-repeater-issue.js

// controller
function MyCtrl() {
  this.instMethod = function() {
    return this.$id;
  };
}

MyCtrl.prototype.protoMethod = function(index) {
  return this.$id;
};

// template
<ul>
  <li ng:repeat="i in [1]">
    {{instMethod()}} == {{protoMethod()}}
  </li>
</ul>