A demo express backend made for CRUD centric applications

api.js

const express = require("express")
const router = express.Router();
const Todo = require("../models/todo")

router.get("/todos", (req, res, next) => {
    Todo.find({}, "action")
        .then(data => res.json(data))
        .catch(next);
})

router.post("/todos", (req, res, next) => {
    if (req.body.action) {
        Todo.create(req.body)
            .then(data => res.json(data))
            .catch(next)
    } else {
        res.json({
            error: "The input field is empty!"
        })
    }
})

router.delete("/todos/:id", (req, res, next) => {
    Todo.findOneAndDelete({ "_id": req.params.id})
        .then(data => res.json(data))
        .catch(next)
})

module.exports = router;

model.js

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

// create a schema
const TodoSchema = new Schema({
	action: {
		type: String,
		required: [true, "The todo text field is required"],
	},
});

// create a model
const Todo = mongoose.model("todo", TodoSchema);

module.exports = Todo;

server.js

const express = require("express");
require("dotenv").config();
const mongoose = require("mongoose");
const routes = require("./routes/api");

mongoose
	.connect(process.env.DB, {
		useNewUrlParser: true,
		useUnifiedTopology: true,
	})
	.then(() => console.log("Database is connected successfully"))
	.catch((err) => console.log(err));

// mongoose promise is deprecated, we override it with node's promise
mongoose.Promise = global.Promise;

const port = process.env.PORT || 5000;
const app = express();

app.use((req, res, next) => {
	res.header("Allow-Access-Allow-Origin", "*");
	res.header(
		"Allow-Control-Allow-Headers",
		"Origin, X-Requested-With, Content-Type, Accept"
	);
	next();
});

app.use(express.json());

app.use("/api", routes);

app.use((err, req, res, next) => {
	console.log(err);
	next();
});

app.listen(port, () => {
	console.log(`Server is running on port ${port}`);
});

This is how we set a header in responses back to the client side javascript:

app.use((req, res, next) => {
	res.header("Allow-Access-Allow-Origin", "*");
	res.header(
		"Allow-Control-Allow-Headers",
		"Origin, X-Requested-With, Content-Type, Accept"
	);
	next();
});

And this is how we handle the error messages (if occurred any) in the backend, using middlewares:

app.use((err, req, res, next) => {
	console.log(err);
	next();
});