Which attacks are possible concerning my security layer concept?

Question

Despite all the advices to use SSL/https/etc. I decided to implement my own security layer on top of http for my application... The concept works as follows:

Answer 1

Javascript encryption can be enough when your adversary is an eavesdropper that can see your traffic but not modify it.

Please note that I am not referring to your specific idea (which I did not take the time to fully understand) but to the general concept of Javascript encryption.