NodeJS create json object from array - arrays

Question

I'm working with some arrays in node and I want to send if as one JSON object to the front-end. I use express to do this. I have a model called User where I find users based on their email. That email is provided in an array. I do get the user object but I can't create one JSON object out of them!
I have tried some middleware but that didn't give me any result! https://www.npmjs.com/package/node.extend
var users = {};
for (var i = 0; i <emails.length; i++) {
User.findOne({
'email': project.students[i]
}, function (err, user) {
if (err) {
res.send(err);
}
// Fill the users object with each user found based on the email
});
}
console.log(users); // Should be one JSONObject
Thanks for the help!

Answer 1

You should be able to do this in a single query. It looks like you're using mongoose, so try something like this:
User.find({ email: { $in: emails } }, function(err, results) {
if (err) return res.send(err);
res.send(results);
});
It's also worth noting that javascript is single threaded. This means that a lot of operations happen asynchronously, meaning you have to wait for the operation to get done before you can move on. Your console logging statement above doesn't wait for the database operation to complete. You have to wait for the callback function to execute.
UPDATE: Also just noticed that you are looping over emails but then using project.students[i] within each iteration. I can't see the rest of your code, but this is just buggy code. You should be either looping over project.students or using emails[i] within each iteration.
UPDATE 2: It appears that you are wanting to send more than just an array of user with the response. So the first goal is to use a single query using the $in operator (see example above - you should be able to pass a list of emails to mongoose). Anything mongo-related, you always want to reduce the amount of queries to the database if you care at all about performance. The second task is to reformat your users and other data accordingly:
var finalResponse = { token: "12341234", users: null };
User.find({ email: { $in: emails } }, function(err, results) {
if (err) return res.send(err);
if (!results.length) return res.send(finalResponse);
// OPTION 1: Array of users (recommended)
finalResponse.users = results;
// OPTION 2: users object, keyed by the users email
finalResponse.users = {};
results.forEach(function(user) {
finalResponse.users[user.email] = user;
});
// FINALLY, send the response
resp.send(finalResponse);
});