On_sent_ok throwing Uncaught referenceError

Hello,

I know it has been asked in the forum for many times, and most of the time I saw that the problem is with JS conflict, I have followed every troubleshoot step suggested by wordpress to resolve this error including deactivating and reactivating each plugin and default theme, but somehow its not working.

All of a sudden today, when I tried to submit my form, the console gave
Uncaught referenceError: firstname is not defined

Now, I know that firstname is the variable I am defining using jQuery for value of a form field in additional setting of my form , but when I try to initialize all variables including this with “var”, it gave another error :
Unexpected token var

I’d appreciate any kind of help from wordpress community.

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