I can only speak for React, but the declarative component model doesn't eliminate state or imperative code, it just nudges you towards separating your stateful code from your layout/rendering code. In the React/Redux convention, your application is one big state machine with transitions encoded in reducers, and your state -> view data transformations in "selectors". View components are composed into one big pure function of state. Putting barriers between those classes of functionality makes it much easier to compose complex behavior from small, focused functions. Obviously you can write code with those properties in any context, but conventional React/Redux architecture makes the lines more explicit, which is why I like it. Lots of people hate it.
