How to return a complex JSON response with Node.js?

Using nodejs and express, I'd like to return one or multiple objects (array) using JSON. In the code below I output one JSON object at a time. It works but this isn't exactly what I want. The response produced isn't a valid JSON response since I have many objects.

I am well aware that I could simply add all objects to an array and return that specific array in res.end. However I am afraid this could become heavy to process and memory intensive.

What is the proper way to acheive this with nodejs? Is query.each the right method to call?

app.get('/users/:email/messages/unread', function(req, res, next) {
var query = MessageInfo
.find({ $and: [ { 'email': req.params.email }, { 'hasBeenRead': false } ] });


res.writeHead(200, { 'Content-Type': 'application/json' });
query.each(function(err, msg) {
if (msg) {
res.write(JSON.stringify({ msgId: msg.fileName }));
} else {
res.end();
}
});
});

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[Edit] After reviewing the Mongoose documentation, it looks like you can send each query result as a separate chunk; the web server uses chunked transfer encoding by default so all you have to do is wrap an array around the items to make it a valid JSON object.

Roughly (untested):

app.get('/users/:email/messages/unread', function(req, res, next) {
var firstItem=true, query=MessageInfo.find(/*...*/);
res.writeHead(200, {'Content-Type': 'application/json'});
query.each(function(docs) {
// Start the JSON array or separate the next element.
res.write(firstItem ? (firstItem=false,'[') : ',');
res.write(JSON.stringify({ msgId: msg.fileName }));
});
res.end(']'); // End the JSON array and response.
});

Alternatively, as you mention, you can simply send the array contents as-is. In this case the response body will be buffered and sent immediately, which may consume a large amount of additional memory (above what is required to store the results themselves) for large result sets. For example:

// ...
var query = MessageInfo.find(/*...*/);
res.writeHead(200, {'Content-Type': 'application/json'});
res.end(JSON.stringify(query.map(function(x){ return x.fileName })));

query.exec(function (err, results){ if (err) res.writeHead(500, err.message) else if (!results.length) res.writeHead(404); else { res.writeHead(200, { 'Content-Type': 'application/json' }); res.write(JSON.stringify(results.map(function (msg){ return {msgId: msg.fileName}; }))); } res.end(); });