Retrieve the value of an ASP.Net text box [duplicated]

I have a textbox with id TextBox and

I have a JavaScript function

function prueba() {
  var hotel = document.getElementById("titulo").innerHTML;
  $('#MainContent_TextBox1').val(hotel);
}

Now in the codebehind I want the value I assigned to Textbox , recover it

 public void printDivs()
 {
   eWidget hotel = new eWidget();
   hotel.titulo = TextBox1.Text;
 }

But when debugeo , it tells me that it has nothing that textbox , although visually if it has