You should never be using frameworks. http://www.catonmat.net/blog/frameworks-dont-make-sense/
Use frameworks when they are appropriate, stand on the shoulders of others who have made significant contributions to the community.
All of the popular modern JavaScript frameworks are easy to learn, increase flexibility and creativity, are themselves mostly high powered versions of the core language (no useless knowledge after learning), generally small, and in no way are Facebook, Google, or Microsoft about to abandon React, TypeScript, Angular et al...
And that's just front end frameworks. Express and Koa do nothing to mystify idiomatic JavaScript or server development, and are just implementations of popular, easy to understand programming patterns.