Functional testing automation using javascript tools

I was looking for easily adoptable functional test (e2e) automation tools using javascript. I did some exploration and picked some (Mocha, Jasmine, nightwatch, and intern). It is mentioned commonly that Mocha, and Jasmine are used for unit test automation, and nightwatch/intern can be used for functional test automation (e2e).

I really don't understand the difference between these tools or what makes them to be categorized under functional or unit test tools? Can't Mocha or Jasmine be used for functional test automation?

Added to that, http://theintern.io/ compares the market leading javascript tools feature wise. "includes functional testing" feature is applicable only for intern and nightwatch. I need clarification that why the same cannot be done in Mocha/Jasmine. Need your expertise answers.

thanks mani