Question: dear all..i have a textfield.
i want after i have typed identity number inside it, the script can identifying to "user table" at DB.
i want if id number not match can show an alert..
how do i do that?i'm newbie at javascript

Answer: 
I'd suggest libmodbus, it works well and is cross platform.

<http://www.libmodbus.org>
I am just starting to explore these options as well. My priority is on ease of use which has led me to [RModBus](http://rmodbus.heroku.com/) since it was the only one that I was able to get immediate results with. However, there is also a Python library, Pymodbus, that appears to be quite complete in implementation. 

I'm sorry, I just figured out that GCC is a compiler; my answer is way off topic.

Again, I was looking for a scripting language that my noob self could be more comfortable in. It really came down to a question of language rather than the library itself. Oh, I am only using the TCP/IP stack at this time, which somewhat simplifies it as well.