What is the type of function in flow javascript type checker?

Question

How would you define type for functions in flow, in the context of function getting passed in as argument? For eg, afterDoneSomething below is callback function that's getting passed - I'm not sure how I define it's type with flow.

function doSomething(path:string, afterDoneSomething:<What is the Type>)

Answer 1

According to the doc: http://flowtype.org/docs/functions.html, you need to supply the type of the function's parameters and returned value: (P1: T1, .., Pn: Tn) => U

So suppose your afterDoneSomething takes a number and return a number, it should be annotated as

function doSomething(path:string, afterDoneSomething: (x: number) => number)