Strange

I agree, somewhere several exit points are even necessary (for example, recursion). But this specific example can be simplified a little, at least for readability.

What are the advantages of "var" over "let"?

Maybe it is better to use var instead of let?

using one exit point from the function

But this saves performance. At one point you check something, and you already know what to return so why calculate all that other stuff you don't need?
It is possible, yes, but it is a fairly common pattern in JS to do this.

A bit hard to read the code. I would also recommend using a single exit point from the function, this helps a lot

I should broke this to 2-3 rows, thanks

My bad

Oh, I didn’t think about performance. Thanks for the advice

Come on, spoiler flags please!

I think const is better