Node.js: How to run asynchronous code sequentially

Question

I have this chunk of code

User.find({}, function(err, users) {
    for (var i = 0; i < users.length; i++) {
        pseudocode
        Friend.find({
              


        

Answer 1

First lets go a bit more functional

var users = User.find({});

users.forEach(function (user) {
  var friends = Friend.find({
    user: user._id
  });
  friends.forEach(function (friend) {
      if (user.websiteaccount !== 'None') {
         post(friend, user);
      }
      sendMail(friend, user);
  });
});

Then lets async that

async.waterfall([
  async.apply(Users.find, {}),
  function (users, cb) {
    async.each(users, function (user, cb) {
      async.waterfall([
        async.apply(Friends.find, { user, user.id}),
        function (friends, cb) {
          if (user.websiteAccount !== 'None') {
            post(friend, user, function (err, data) {
              if (err) {
                cb(err);
              } else {
                sendMail(friend, user, cb);
              }
            });
          } else {
            sendMail(friend, user, cb);
          }
        }
      ], cb);
    });
  }
], function (err) {
  if (err) {
    // all the errors in one spot
    throw err;
  }
  console.log('all done');
});

Also, this is you doing a join, SQL is really good at those.