My original post was:

I'm new to jquery, but i think with document.getElementById( "TextBox1" ); you don't use jquery. Try $("#TestBox1") instead. ASP.NET Objects are rendered as normal HTML, because of that jquery should find these elements. you can check the generated html and if the textbox has an id attribute it should work.

 

When I use $("#TextBox1")

 

I get an error "object expected".