Slowdown due to non-parallel awaiting of promises in async generators

Question

I\'m writing code using generators and Bluebird and I have the following:

var async = Promise.coroutine;
function Client(request){
    this.request = request         


        

Answer 1

The answer by Benjamin Gruenbaum is correct, but it loses the generators aspect completely, which tends to happen a bit when you're trying to run multiple things in parallel. You can, however, make this work just fine with the yield keyword. I'm also using some extra ES6 features like destructuring assignments and object initializer shorthand:

Client.prototype.fetchCommentData = async(function* (user){
    var country = countryService.countryFor(user.ip);
    var data = api.getCommentDataFor(user.id);
    var notBanned = authServer.authenticate(user.id).then(function(val){
        if(!val) throw new AuthenticationError(user.id);
    });

    // after each async operation finishes, reassign the actual values to the variables
    [country, data, notBanned] = yield Promise.all([country, data, notBanned]);

    return { country, data, notBanned };
});

If you don't want those extra ES6 features being used:

Client.prototype.fetchCommentData = async(function* (user){
    var country = countryService.countryFor(user.ip);
    var data = api.getCommentDataFor(user.id);
    var notBanned = authServer.authenticate(user.id).then(function(val){
        if(!val) throw new AuthenticationError(user.id);
    });

    var values = yield Promise.all([country, data, notBanned]);

    return { 
        country: values[0], 
        data: values[1], 
        notBanned: values[2]
    };
});