What tech stack to use for users in environments with bad internet?

I'm building a web app where many of the users' access to the internet will often be sporadic and low speed. I'm wondering what kind of stack is best suited for this situation? Is a client-side JS framework a no-no? Should I prioritise performance when choosing a backend language? How would one run the servers? Which database technology?, etc. The app itself should be a fairly simple CRUD app but will require loading lots of images, files, etc.