how javascript invoke a method from ocx?

[yli116]

i have an ocx method like this:

BOOL WINAPI getKeySN(
IN DWORD idx，
OUT BYTE* SN，
INOUT DWORD * SNLen);

i wanna get the SN, how to do it in javascript?
and what do all these in, out and inout mean anyway?
i am a new one on javascript..
thanks!