Defining types for arrow functions

Finally, let's see how types would be defined for arrow functions. We can have a couple more implementations of the toString() function we saw earlier in the Basic types in Flow section:

// Source file: src/types_basic.js

const toString2 = (x: number): string => {
    return x + "";
};

type numberToString = number => string;
const toString3: numberToString = (x: number) => String(x);