JS \ Press Enter

I have an input textbox in a webpart and a label output. 

I use updatepanel to fill label when i input smthng into textbox without postback (while still having heavy server side query).

Now everything is fine, but i have to press ENTER in order to fill label with data.

So how do i:

1. Send ENTER thru javascript when i input smth into textbox

or

2. Invoke this AJAXPOSTBACK when i input smth into textbox. So that page wont refresh.

If i do

TextBox1.Attributes["onkeydown"] = "__doPostBack('TextBox1', '');";

then real postback happens and text is rolled back from previous state.