Express middleware to configure response - node.js

Question

I want to create a middleware that automatically formats my output and returns it in a format that looks like
{
"successful": "true",
"message": "Successfully created",
"data": {
"name": "Joe",
"year": 1
}
}
Currently I'm just returning a json of the data itself (name, year, etc.)
I want to add the "successful", "message", etc.
Here's some snippets of my code below:
routes/student.js
var student_controller = require('../controllers/studentController');
router.get('/list', student_controller.student_list);
controllers/student.js
var Student = require('../models/student');
exports.student_list = function(req, res, next) {
Student.find()
.exec(function(err, list_students) {
if (err) {return next(err);}
res.json(list_students);
});
};
app.js
var studentRouter = require('./routes/student');
app.use('/student', studentRouter);
How do I make this middleware, and in which file(s) should I be calling it?

Answer 1

The response can be intercepted by overriding response.json function. By doing so, and adding our custom function, every time, response.json() is called, our intercepting function is triggered.
middleware/response.filter.js:
// Response Interceptor Middleware
export default (request, response, next) => {
try {
const oldJSON = response.json;
response.json = (data) => {
// For Async call, handle the promise and then set the data to `oldJson`
if (data && data.then != undefined) {
// Resetting json to original to avoid cyclic call.
return data.then((responseData) => {
// Custom logic/code. -----> Write your logic to add success wrapper around the response
response.json = oldJSON;
return oldJSON.call(response, responseData);
}).catch((error) => {
next(error);
});
} else {
// For non-async interceptor functions
// Resetting json to original to avoid cyclic call.
// Custom logic/code.
response.json = oldJSON;
return oldJSON.call(response, finalResponse);
}
}
} catch (error) {
next(error);
}
}
In the Server.js file, register the middleware:
// Server.js file
import externalResponseFilter from "./middleware/response.filter.js:";
// Create Express server
const app = express();
// Response interceptor - Initialization.
app.use(externalResponseFilter);
And in the controller where you are returning the response, return with response.json() function instead of response.send().
Let me know if any additional explanation is required.

Answer 2

I think there is no need to middleware in your case unless you need an auth check for this routing. The Middleware has the functionality to handle something before getting your response.
your code shall be:
router.get('/list',(req,res,next)=>{
Student.find().then(data=>res.json(data)).catch(err=>conole.log(err)) });