I was hoping it shows that it really depends on your style (procedural or functional). Thanks to generators and arrow functions, ES6 lets you write code using either.
When you're writing in functional style, you'd use arrows, which work nicely both for small lambdas and for writing combinators that can be partially applied. When you're writing in a more procedural style, generators are your "do syntax" equivalent(-ish):
async(function* getCredentialsByToken(token) {
credentials = yield NewCredentials(token)
return User.findByName(credentials.userName)
});