Q:

How to resume normal scrolling after: window.onscroll = function () { window.scrollTo(0, 0);

I have a panel that opens but on IOS the body is scrolling behind the panel. 
I am using window.onscroll = function () { window.scrollTo(0, 0); to stop the page scrolling behind the panel when the panel is open. 
However, I need to resume normal scrolling afterwards in an event handler.  What javascript can I use to resume normal scrolling?  as currently when the panel is closed when you try to scroll you get positioned back to (0,0) of the window. 
Thank you! 

A:

When the panel is opened you set the onscroll function
window.onscroll = function () { window.scrollTo(0, 0);}

when the panel is closed:
window.onscroll = null;

