var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.");
var t0 = performance.now();
var t1;
doSomething().then(result => {
t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.");
});