Flow won't infer types of arbitrary Javascript libraries. It will let you use them as untyped values, just like Typescript does when you set the allowJs option.

Flow won't infer types of arbitrary Javascript libraries. It will let you use them as untyped values, just like Typescript does when you set the allowJs option. (I've used Flow for a long time. I'm starting to transition a large codebase from Flow to Typescript, and I'd highly recommend anyone to just start with Typescript rather than Flow. Flow's type inference isn't all that useful, and causes Flow to be magnitudes slower than Typescript. In a large codebase, it can take Flow tens of seconds to minutes to react to a code change and show you errors or auto-completions in your code after typing in an editor, compared to practically instantaneous updates with Typescript.)