I'm using reagent's create-class and I need to access a value create in :component-did-mount in :component-will-receive-props. What's the best way to get it there? Should I put it in an atom?

yup

should probably be a ratom if your render fn depends on it (though be careful to avoid infinite loops)

you may also split the component into an outer (side-effecting) and inner (pure) component

out of curiosity, what's the use case?

@pesterhazy I'm reagentizing codemirror: https://github.com/dashmantech/reagent-toolbox-playground/blob/master/src/cljs/reagent_codemirror/core.cljs

Cool