Debug a (probably) javascript issue

We have a browser based client Written in HTML5/Javascript connecting to a Server app written in C++. In the latest version: - Using Chrome, you input username/password & all works fine. Logged on and you can work. - Using Firefox, you do the same... now takes a VERY long time to connect but eventually you log on & works ok - But using Safari, now gives "'undefined' is not a constructor" error and will not allow logon. In previous version all three browsers worked fine but new code has been added to new version. This is therefore a LOGIN issue that stops logon in Safari and is slowing the login process down in Firefox. I THINK the issue is a javascript (client) issue though it could also be a C++ issue(gateway). I am looking for someone to go through the code, debug, find and correct the error. The code will remain on our server and you will be able to connect via team viewer only.