How to assign value of a javascript variable to a perl variable

I'm new to CGI and javascript.

I have a javascript variable which has a value assigned.

my var = getHTML();

I want to use this value in perl script.

$input_string = "var";  - is this possible?

I know a way we can do - using form and submit action to pass the
javascript variable to the perl script. Is there a way I can avoid
using a click of button as an intermediate step. Passing the value as a
query string has a restriction of 1024 characters. I have content which
could be 3000 characters or more.