Timing async calls with promises

timed.js

const now = () => new Date().getTime();
const timed = (promise, key = 'delta') => {
	const start = now();
	return promise.then(data => ({
		...data,
		[key]: now() - start
	}));
}

const test = () => {
	const myFakeAsync = () => new Promise(res => setTimeout(res.bind(null, { message: 'hello'}), 1337));
	return timed(myFakeAsync());
}

// use `babel-node --stage=0`
test().then(console.log.bind(console));
// --> { message: 'hello', delta: 1341 }