Detect if API loaded OK in JS ?

In my app, I would like to detect if the API loaded OK.
It might not if, for example, the wrong key was specified.

now my app will run ok with a bad api key up to the line
map = new GMap(document.getElementById("div_map"))
at which point it fails.

is there any JS command I can run to detect if that command will fail ?
I tried seeing if there was a return value to the map init command but
it never gets there with a bad api key.