function types Typescript or flow

functions.ts

// Function that executes a action and dont receive any params and returns void
type ChangesSomething = () => void

// Function that receives a string and returns a string
type FormatName = (name: string) => string

// Function that checks if a string is null and returns a boolean
type CheckNull = (value: string) => boolean

// Function that sums two numbers and returns a number
type Sum = (n1: number, n2: number) => number