Danke you for the clarification

We're playing the code golf (https://en.wikipedia.org/wiki/Code_golf) game, tl;dr write a solution with the minimal number of characters. Yes, in real, production code, you'd use const or let (var is still valid, but most modern code uses let unless var is absolutely necessary, since it has slightly different behavior https://stackoverflow.com/a/11444416/12101554), but this is still valid JavaScript.

Use const, let or var!!!

Why would it be slower? Not that performance matters when you are doing code golf.

It will shave a few bytes but on the other hand the time of execution will be longer

You can omit the ; and replace && with & to shave a few bytes