GJS : How can I use Regex ( parse HTML ) ?

Hello,

I download a page and I want to parse it so I can get specific data from 
it. Unfortunately, I didn't find any ready-made library ( in GJS ) for 
HTML parsing, so I turn to regular expressions.

Because the documentation doesn't help me at all, can you please tell 
me, how I can use the regular expressions in GJS ?

( my code is not running because I don't use the GJS regex library 
properly )

Thanks in advance for your time.
Anastasios.