Request body transformation in Express - Mini Project: Build & Apply

Request Body Transformation in Express

📖 Scenario: You are building a simple Express server that receives user data in JSON format. You want to transform the incoming request body to add a new field before processing it further.

🎯 Goal: Build an Express server that accepts JSON data in a POST request, transforms the request body by adding a new field receivedAt with the current timestamp, and then sends back the transformed data as JSON.

📋 What You'll Learn

Create an Express app with JSON body parsing middleware

Add a POST route at /submit to receive JSON data

Add a receivedAt field with the current ISO timestamp to the request body

Send the transformed request body back as JSON in the response

💡 Why This Matters

🌍 Real World

Transforming request bodies is common in APIs to add metadata or normalize data before processing.

💼 Career

Backend developers often need to manipulate incoming data in Express servers to prepare it for storage or further logic.

1

Setup Express app and JSON middleware

Create an Express app by requiring express and calling express(). Use app.use(express.json()) to enable JSON body parsing.

Express

const express = require('express');
const app = express();
// Your code here

Need a hint?

Use express.json() middleware to parse JSON bodies automatically.

2

Add POST route at /submit

Add a POST route handler on app for the path '/submit' using app.post('/submit', (req, res) => { ... }).

Express

const express = require('express');
const app = express();
app.use(express.json());

// Your code here

Need a hint?

Use app.post to create a POST route at /submit.

3

Transform request body by adding receivedAt

Inside the POST route handler, add a new field receivedAt to req.body with the current ISO timestamp using new Date().toISOString().

Express

const express = require('express');
const app = express();
app.use(express.json());

app.post('/submit', (req, res) => {
  // Your code here
});

Need a hint?

Use new Date().toISOString() to get the current time in ISO format.

4

Send transformed body as JSON response

Send the transformed req.body back as JSON in the response using res.json(req.body).

Express

const express = require('express');
const app = express();
app.use(express.json());

app.post('/submit', (req, res) => {
  req.body.receivedAt = new Date().toISOString();
  // Your code here
});

Need a hint?

Use res.json() to send a JSON response.