Functional frontend. How Elm makes frontend developers happier?

Elm a niche frontend technology. Why do teams as different as a education startup, freelancers from Izrael, a big Swedish newspaper and the AWS team reach for it?

How is Elm different from JS/TypeScript/Java and React/Angular? How are Elm applications architected? Why are Elm programmers happier? What are the challenges of working with it? I will answer these and other questions.