One potential workaround could be to add "dummy" fields to the form with default values of the variables you need in the custom scripting. (*) Then assign CSS classes to these for referencing purposes, hide the fields with CSS, and you can access the values by referencing the hidden fields. The only caveat would be if, as Xiang mentions in the thread Junaid linked, the value of the variable hasn't yet been processed in the backend, in which case you might obtain null or unexpected data.

If the variables you'd need to reference are related to current date, submission time, etc., I would recommend using built-in Date objects in JavaScript which would probably be less overhead to work with.

Hope this helps!

(*) If the variable you want to access was from a prior submission in the process, to avoid variable bloat you can just add that same variable to the form.