Callback Hell

hell.js

app.get('/loadUserData', function(req, res) {
	var keys, chats, messages;
	var u_id = req.query.user_id;

	db.all(`SELECT * FROM keys WHERE user_id = ` + u_id + ` OR expired_at IS NULL`, function(err, data) {
		if(err || !data) return res.status(404).send(err || "No data found for ID");
		keys = data;

		db.all(`SELECT * FROM messages WHERE recipient_id = ` + u_id, function(err, data) {
			if(err || !data) return res.status(404).send(err || "No data found for ID");
			messages = data;

			db.all(`SELECT * FROM chats WHERE chat_id IN (SELECT chat_id FROM user_chat WHERE user_id IS ` + u_id + `)`, function(err, data) {
				if(err || !data) return res.status(404).send(err || "No data found for ID");
				chats = data;
				var chatsProcessed = 0;

				db.serialize(function() {
					for (let chat of chats) {
						db.all(`SELECT user_id, first_name, last_name FROM users WHERE user_id IN 
						(SELECT user_id FROM user_chat WHERE chat_id IS ` + chat.chat_id + `)`, 
						function(err, data) {
							if(err) return res.status(404).send(err);

							chat.members = data;
							chatsProcessed++;
							if(chatsProcessed == chats.length) {
								return res.send({
									"keys": keys,
									"messages": messages,
									"chats": chats
								});
							}
						});
					};
				});
			});
		});
	});
});