As you were already told when you asked the same question in the chat, WWW::Mechanize does not support Javascript, just like the error message says.

Also, in the chat, you were pointed towards:

Typing "WWW::Mechanize Javascript into the "Search" box on this site yields many more informative posts about the topic.

Updated link as per ikegami's reply below

In reply to Re: JavaScript Plugin in www::Mechanize by Corion
in thread JavaScript Plugin in www::Mechanize by venkatesan_G02

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