Using jQuery and AJAX process a form with PHP
On client-side, some small points ...


Avoid more $(selector) phrases than absolutely necessary. Inside the submit handler, you can use $(this), which will be faster.
Pass serializedSubmission formally to the subroutines rather than rely on an outer var.
The outer var responseObjcan't be reliably used except in an asynchronous context, so if you want to cache anything, cache the promise returned by $.ajax(), not the data.
Needs less obvious comments and more on things that matter, eg against lines like if (temp.search('=&amp;') &gt; 0 || temp.slice(-1) == '='), which I had to study to work out the validation strategy. Maybe a few words would have helped me.