Many refer JS as a necessary evil. It can help in making the websites more interactive and interesting while introducing potential problems due to negligible or no validation of its working on the server end. Although several standards and protocols have been created for the safe execution of JS like Sandbox Environment, Strict Mode, Same origin request policy, etc it still remains as a potential gateway to exploit negligent or non careful users.
This chapter was originally written by Konrad "Unrooted" Klawikowski and additions were made to it by Gadila Shashank Reddy. For the original content written by Konrad, see here.