Your sleep function does not work because setTimeout does not (yet?) return a promise that could be awaited. You will need to promisify it manually:
function timeout(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function sleep(fn, ...args) {
await timeout(3000);
return fn(...args);
}
Btw, to slow down your loop you probably don't want to use a sleep function that takes a callback and defers it like this. I recommend:
while (goOn) {
// other code
var [parents] = await Promise.all([
listFiles(nextPageToken).then(requestParents),
timeout(5000)
]);
// other code
}
which lets the computation of parents take at least 5 seconds.