CODEWITHSUNDEEP
javascriptflowtype
Max
Max

Reputation: 11

Flow Typechecking Questions

I'm new to Flow and am wondering why a couple 'basic' issues don't raise any warnings in Flow:

  let foo: Array<{| id: string, occursOn: string |}>;
  foo = [{ id: "5", occursOn: "2017-01-01" }];

  // Not a flow error!
  console.log(foo[0][0].bar);

  const grouped = groupBy(foo, "occursOn");

  // Not a flow error!
  console.log(grouped["2017-01-01"].bar);

Why is accessing foo[0][0].bar ok in Flow, when I have been explicit about the type of foo?

Similarly, I have lodash installed via flow-typed, yet grouped["2017-01-01"].bar seems to be totally fine in Flow?

Upvotes: 1

Views: 41

Answers (1)

loganfsmyth
loganfsmyth

Reputation: 161467

Your first example with the array index seems like this bug: https://github.com/facebook/flow/issues/4257

For the groupBy, most likely you just haven't told Flow what groupBy does. I'd assume you're doing

import { groupBy } from 'lodash';

and by default Flowtype doesn't have any way to know what the lodash module is or what its functions do, so you need to install type definitions for Lodash, and hope that you're not using too much runtime magic so it'll give you a reasonable type signature.

For your case, you do get the error when Flow knows what type it is, which you can see here.

Upvotes: 1

Related Questions