I am learning how to implement Bootstrap modals in AngularJS. I can do it when the modal code (the actual popup window code) is on the main page, but I want to be able to display external files so that my SPA isn't super-cluttered.  I am implementing this on a much larger scale, but for simplicity's sake I'll keep the code example to a minimum.

    <html>
      <head>
        <meta charset='utf-8'>
        <script src="js/angular.js"></script>
        <script src="js/angular-ui-bootstrap-modal.js"></script>
        <script src="js/app.js"></script>
        <link rel="stylesheet" href="css/bootstrap.css">
      </head>
      <body ng-app="MyApp" ng-controller="MyCtrl">
    
        <button class="btn" ng-click="open()">Open Modal</button>
    
        <!-- want this code to be an external.html file -->
    
        <div modal="showModal" close="cancel()">
          <div class="modal-header">
              <h4>Modal Dialog</h4>
          </div>
          <div class="modal-body">
              <p>Example paragraph with some text.</p>
          </div>
          <div class="modal-footer">
            <button class="btn btn-success" ng-click="ok()">Okay</button>
            <button class="btn" ng-click="cancel()">Cancel</button>
          </div>
        </div>
    
        <!-- -->
    
      </body>
    </html>

**app.js**

    var app = angular.module("MyApp", ["ui.bootstrap.modal"]);
    
    app.controller("MyCtrl", function($scope) {
    
      $scope.open = function() {
        $scope.showModal = true;
      };
    
      $scope.ok = function() {
        $scope.showModal = false;
      };
    
      $scope.cancel = function() {
        $scope.showModal = false;
      };
    
    });

I know that I need to add a `templateUrl` to my app.js, but don't know how I would bridge the gap between the three files (index.html, app.js, and external.html).