Flow annotations

You have to start each file with // @flow as the first comment line.

1. Classes

Declare properties

It is necessary to define each used property. This not only helps in type analyzation but also to make it more readable:

// @flow
class SchemaAny {

  data: any

  constructor(data: any) {
    this.data = data
  }
}

Command concatenation

If this should be done, don´t define the return type as the current class. Better use this as return type which will also work if a subclass calls methods from it´s superclass:

/* @flow */

class A {
  x(): this {
    return this;
  }
}

class B extends A {
  y(): this {
    return this;
  }
}

var w = new B();

w.x().y();

Uncheck by casting with any

It's not a very nice solution, but you can cast an object to any. And no unsafe any will be leaked.

/* @flow */

class A {
  get clone(): this {
//    return Object.assign(Object.create(this), this) // flow error
    return Object.assign((Object.create(this): any), this)
  }
}

class B extends A {}

var b = new B()
var c = b.clone

Here the Object.create(this) will normally give an error: Covariant property clone incompatible with contravariant use in call of method assign.

The fix is it is casted by any.