clear() does not work as intended

[jhnns]

Hi 👋,

first of all: thanks for this library ❤️

I noticed that clear() does not always remove all keys. This happens when there's another key in the SessionStorage that does not have the store prefix (in my case it was a browser extension).

The current implementation iterates over all keys and removes them if they have the store prefix. The remove operation, however, might mess with the order of keys that are returned by key(i). In my case, key(i) returned the same key for a different i. MDN writes about key():

The order of keys is user-agent defined, so you should not rely on it.

The current implementation can be fixed by first getting all the keys via Object.keys() and then iterating over that array. Object.keys() has good browser support these days but I don't know if that's ok for you. You could also iterate with for ... in.

Are you interested in a fix with Object.keys()? I could send a PR.