Update JS so frontend renders in IE9

"screen" collides with an existing reserved word in IE9.  This causes an error "SCRIPT5039: Redeclaration of const property" on line 19, preventing the JS code from compiling and running.

Changed to non-reserved word "thescreen".  Tested OK on IE9 (NOT compatibility mode!), Chrome, Firefox.

Fixes Issue #379
Merge pull request #756 from android606/master

Update JS so frontend renders in IE9