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.

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.

length can be renamed to width to better match another constant