[re]

Here's a console command you can run to increase the snake length immediately, and thus the difficulty:

   (() => { let count = 50; const delay = 100; const interval = setInterval(() => { addSnakeNode(); if (--count <= 0) clearInterval(interval); }, delay);})()

[londons_explore]

Why wrap in a lambda?

[re]

Because I learned JS before ECMAScript 6 was widely supported by browsers and haven't written a ton of it targeting modern browsers. You're right that it's unnecessary.

[tinyhitman]

Could be to allow use of local variables that do not leak into the scope this code is executed in. That's what I use this pattern for.