title: How does $injector service inject itself in AngularJS
body: <p>An AngularJS app depend on the $injector service to inject other built-in or customize services in controller,directive or other injectable things, but how $injector service inject itself,just like :  </p>
  
  <pre><code>app.controller(function($injector,$scope){
  
  //...
  
  });
  </code></pre>