Question about the syntax of a function in Node.js - node.js

Question

I am following a tutorial to make a blog, and for the MongoDB connection in the server.js file, the instructor made a boiler connection function withDB. Operations and res are props of withDB function. In line 6, is operations a function passed a prop of the withDB functions?
Below is the withDB function.
const withDB = async (operations, res) => {
try {
const client = await MongoClient.connect('mongodb://localhost:27017', { useNewUrlParser: true });
const db = client.db('my-blog');
await operations(db); // is operations a function that takes db as its props?
client.close();
} catch (error) {
res.status(500).json({ message: 'Error connecting to db', error });
}
}
Using withDB in a function
app.get('/api/articles/:name', async (req, res) => {
withDB(async (db) => {
const articleName = req.params.name;
const articleInfo = await db.collection('articles').findOne({ name: articleName })
res.status(200).json(articleInfo);
}, res);
})

Answer 1

yes actually operations is your callback function, you call it with db as param once you initialize your database connection.
Maybe you're not comfortable with ES6 arrow function syntax. you can find in Mdn doc a simple example with old regular function, and in your case it could be :
function findArticlesByName(articleName) {
return function(db) {
return db.collection('articles').findOne({ name:
articleName });
}
}
async function withDB(callback) {
try {
const client = await MongoClient.connect('mongodb://localhost:27017', { useNewUrlParser: true });
const db = client.db('my-blog');
return callback(db);
} catch (error) {
throw new Error({ message: 'Error connecting to db', error });
} finally {
client?.close();
}
}
app.get('/api/articles/:name', async (req, res) => {
try {
const articleInfo = await withDB(findArticlesByName(req.params.name));
res.status(200).json(articleInfo);
} catch(error) {
res.status(500).json(error);
}
})
Conclusion, you could easily inline your callback function like in your example, but maybe it's more understandable that way.
Moreover, you should avoid to use a wrapper in order to create and close your db connection after each request, because it could occur some weird errors. Databases connections or any resource-intensive tasks should be shared as much as possible.
So a better solution is to create a specific class with the default implementation of your singleton, construct a single instance of your connection at the top of your app, pass the single instance into each module that needs it then close your connection just before exiting your app.
Hope it'll help.