POS Qweb template extended. How to find new element added in it - odoo v8

Hello all,

I have extend the one of the Qweb template ('Orderline') and add my element (a drop down <select> ... </select>). Now I extended the PosWidget in javascript, but I am not able to find that element. I need to add the onchange method on it to perfom some calculations.

Can any one guide me how to find that element which is been added in that template. The problem is that it is not in new template but by extending I have added my element in it. It displays on the screen, but I am not able to access it my javascript code.