Hello. What kind of obfuscations could it be:
<script>var s0 = '';var s1 = '1c4fcm8dS';s0 = interfaces.jsFunction(s1);</script>
I think it doesn't have much sense. Is "interfaces" a special keyword?

Not knowing whether "interfaces" is some system defined function or keyword I would assume that .jsFunction(...) is a decryption function.
Easy to find out. Rip the js code and echo s0 after execution of jsFunction. You will see what jsFunction is doing.

Or even better, directly look at jsFunction. Must be defined somewhere, right !?

Regards,
OHPen