ES7's async/await syntax.

1-sleep-es7.js

// ES7, async/await
function sleep(ms = 0) {
  return new Promise(r => setTimeout(r, ms));
}

(async () => {
  console.log('a');
  await sleep(1000);
  console.log('b');
})()

2-sleep-es6-promise.js

// ES6, native Promises, arrow functions, default arguments
function sleep(ms = 0) {
  return new Promise(r => setTimeout(r, ms));
}

console.log('a');
sleep(1000).then(() => {
  console.log('b');
});

// or if we were to be strictly identical, an "async" function returns a
// Promise, so this is more accurate, but the fluff isn't needed for in this case

(function() {
  return new Promise((resolve, reject) => {
    sleep(1000).then(() => {
      console.log('b');
      resolve();
    });
  });
})();

3-sleep-es6-just-promise.js

// ES6, native Promises ONLY
function sleep(ms) {
  ms = ms || 0;
  return new Promise(function(resolve) {
    setTimeout(resolve, ms);
  });
}

(function() {
  console.log('a');
  sleep(1000).then(function() {
    console.log('b');
  });
})();

4-sleep-es5.js

// ES5, nothing special
function sleep(ms, callback) {
  ms = ms || 0;
  setTimeout(callback, ms);
}

(function() {
  console.log('a');
  sleep(1000, function() {
    console.log('b');
  });
})();

Do we need the reject callback inside a promise?
The below code seems to be working out for me, it catches any error and instead of rejecting it returns null in the resolve function.
Is this bad code, if so why?

function fecthDB() {
	return new Promise((resolve, reject) => {
		try {
			db.query('SELECT * FROM users' (err, result) => {
				if (err || !results) {
					return resolve(null)
				}
				resolve(result)
			})
		} catch (e) {
			resolve(null)
		}
	})
}

function async getUsers() {
	var users = await fecthDB()
	if (!users) { // error handling
		return console.log('error')
	}
	console.log(users) // got users
}