In short: No.
A bit longer: It's not needed. If it's just a simple JScript function, why don't you just copy it? If you want to release the script to the public, you'd better ask the developer of the script you're copying from if you want to use it, but for personal use I don't see any problem. And if that's not the case, why don't you simply modify the script itself instead of trying to inherit its functions? I don't see the point...
EDIT: Holy crap, I'm as slow as hell these days!
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