void 0 !== b &&
//node testability hack
(b.tcg = c);
I don't know if OP is reading this thread, but this is a minified and then beautified version of `if (b !== undefined) b.tcg = c`.
tl;dr is that you can actually redefine the keyword `undefined` since its actually a global property and not reserved. void 0 will always return you the true value of undefined so it will work in all cases regardless of external shenanigans. Pretty neat.
[1] https://stackoverflow.com/questions/7452341/what-does-void-0...
This is horrible :(
However you can still declare variables named undefined that get their own storage and so can have any value. Originally “undefined” didn’t exist in the global scope so many sites had “var undefined” or function f(..., undefined){..} to get a reference to the value.