Serialization

• Serialization is the process of converting data (like objects, arrays, or other complex structures) into a format that can be easily sent over the network or stored in a file/database — typically as a JSON string.
• In Express.js, this usually happens when sending a response using res.json() or res.send().

Example:

const user = { id: 1, name: "Vivek" };
res.json(user); // Serializes 'user' object to JSON format and sends it

Deserialization

• Deserialization is the process of converting serialized data (like a JSON string) back into a JavaScript object.
• In Express.js, this usually happens when reading incoming request data — typically parsed by express.json() middleware.

Example:

app.use(express.json()); // Parses incoming JSON requests into JS objects

app.post("/user", (req, res) => {
  const userData = req.body; // Deserialized data
  console.log(userData);
  res.send("User received");
});

How It Works Together in Express.js

• Serialization happens when sending a response.
• Deserialization happens when receiving and parsing a request body.

Complete Example:

const express = require("express");
const app = express();

app.use(express.json()); // Deserializes incoming JSON

app.post("/user", (req, res) => {
  // Deserialized object
  const user = req.body;

  // Serialize and send it back
  res.json({
    message: "Received user data",
    user: user
  });
});

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

Parsing Form Data [express.urlencoded()]

express.urlencoded() is a built-in middleware function in Express.js used to parse incoming requests with URL-encoded payloads — typically from HTML form submissions.

When a form is submitted using:

<form method="POST" action="/submit">
  <input type="text" name="username" />
  <button type="submit">Submit</button>
</form>