The reason why I want to do that is that when I developing I like to make sure that both my server side(C#) validation is working correctly. So I like to see both the client side and server sides errors to show up.
So while I am testing I have a flag in my jquery validate stuff that just always lets invalid data go through. This way I see the client side and server errors at one go.
However right now I have to manually go and change back and forth when going from development to production.
location.hostname variable gives you the current host. That should be enough for you to determine which environment you are in.
if (location.hostname === "localhost" || location.hostname === "127.0.0.1") alert("It's a local server!");