Flow: make a key from an imported object type optional

Question

I want to import a random object from an external module and use their flow type:

export type randomType = {
    a: string,
    b: boolean
}

I want to import the randomType to my library but I want to make b optional

import { randomType } from 'randomModule';
// pseudo flow code:
type shrinkedRandomType = randomType - {b: boolean}
// How can I make this in flow so it equals this?
type shrinkedRandomType = {
    a: string,
    b?: boolean
}
// or even 
type shrinkedRandomType = {
    a: string
}

Answer 1

The spread operator to the rescue!

If you are unfamiliar with the spread operator, look it up on MDN

Otherwise, the way to do it would be as follows:

type randomType = {
    a: string,
    b: boolean
}

type shrinkedRandomType = {
    ...randomType,
    b?: boolean
}

// Perfectly valid
let test:shrinkedRandomType = {
 a: "Hi"
}