Flowtype "Not covered by Flow" on object property chains
I'm trying to use Flow, but I keep getting the "Not covered by Flow" warning, so my code is mostly underlined. I checked the Flow documentation, but it wasn't helpful regarding object property chaining, so how do you get something like this to work?
It appears that you are using a library that does not have type definitions.
With property lookups where the object is defined within the file, Flow has 100% code coverage without any types at all:
const foo = { bar: { baz: 2 } };
foo.bar.baz;
// 100% Flow coverage
Same goes for separate files:
1.js
// @flow
export default { bar: { baz: 2 } };
2.js
// @flow
import foo from './1.js'
foo.bar.baz;
// 100% code coverage
However, as soon as something is being imported from a file that Flow does not run on (either because it has flow turned off or because its a third-party library that does not use flow), Flow is not able to cover it.
1.js
// @noflow
export default { bar: { baz: 2 } };
2.js
// @flow
import foo from './1.js'
foo.bar.baz;
// 0% code coverage
In order to fix this, you need to give Flow information about the types.
You can do a couple of different things
a.js covered by Flow. a.js.flow file that declare 's the types flow-typed/a.js file that adds declarations. Hopefully this is helpful enough to give you at least a starting point
I'm new to Flow as well, but heres my take:
If you have two classes, A and B, and flow typechecking is not enabled on A, then B functions that call into it will be "uncovered".
// a.js
class A {
}
// b.js
/* @flow */
import A from './A'
class B {
buildA():void {
new A() // I'm un-covered by Flow!
}
}
Flow doesn't know anything about the structure of A, and so therefore can't provide any guarantees.
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