Substring Syntax In Javascript

Trying to debug someone else's javascript code. There is a line that

looks like this:

req = req.substring(req.length-2, req.length);

From what I can gather in their comments, they want to capture the last two characters of the string "req".

I'm guessing that the above line won't do that, and they want to change it to

req = req.substring(req.length-1, 2);

In other words, the parameters are starting position, and length. Is that correct?