From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const
This declaration creates a constant whose scope can be either global or local to the block in which it is declared.
Global constants do not become properties of the window object, unlike var variables. An initializer for a constant is required; that is, you must specify its value in the same statement in which it's declared (which makes sense, given that it can't be changed later).
To answer your 2nd question, global variable can be accessed through window object. However, there is an exception for const.
