Microsoft Dynamics 365 Sales Online: access input element that underlies the control

I am using Microsoft Dynamics 365 Sales Online and I want to get DOM element from XRM.Page object using JavaScript. So, how can I get access to input that is underlies the control (or attribute) element got from Xrm.Page.getContext("any name") or Xrm.Page.getAttribute("any name"). Thank you for the hints in advance!