title: ASP.NET TextBox's OnTextChanged server event should fire some client code before going to server
body: <p>My UserControl has a TextBox, that is subscribed to OnTextChanged event. However, since a lots of business logic and integrations happens on server, I want to disable a form while postback is being performed with some client-side javascript and I'm not sure how to achieve it the right way. </p>
  
  <p>Can I solve this with ClientScriptManager.GetPostBackEventReference?</p>
  
  <p>Edit: as my question seems to be misunderstood:</p>
  
  <p>TextBox is subscribed to event OnTextChanged="tb_TextChanged" which will result on client in onchange=__doPostBack('tb') so I want to inject my javascript disableForm() to onchange DOM event. I know how to implement disableForm(), the question is how to inject my javascript properly?</p>