在flowtype中细化“ any”类型

Question

I seem to be misunderstanding how flowtype refinements work (or maybe my Nuclide/Atom + Flow setup is being dumb). I'd like to do something like the following:

async function getIp(): Promise<string> {
  const resp = await fetch('https://httpbin.org/ip')
  const json = await resp.json() // `json: any` at this point
  if (typeof json.ip === 'string') {
    return json.ip
  } else {
    throw new Error("Weird response.")
  }
}

I'm fetching some JSON from an API endpoint, and it has type any . I'd like to sanity check that it has the right form (eg that it has a string ip field). Nuclide however warns me that every use of json in the above code is "Not covered by flow", including the entire json.ip expression. Why is that? I would have expected the typeof check to refine the type of json.ip to string .

Is there another way to refine untyped values?

Edit: Here's a tryflow example of what I'm seeing.

Answer 1

No, you can't refine any . You already can do anything with it, so what's the point?

If you want Flow to verify your code you should immediately convert your any to mixed :

const json: mixed = await resp.json()