How to Send Response in Express: Simple Guide

In Express, you send a response to the client using the res object methods like res.send() for text or HTML, and res.json() for JSON data. These methods end the response and send data back to the browser or client.

Syntax

Express response methods use the res object passed to your route handler. Common methods include:

• res.send(body): Sends a response body as string, buffer, or object.
• res.json(object): Sends a JSON response with correct headers.
• res.status(code): Sets HTTP status code before sending response.

These methods end the response automatically.

javascript

app.get('/path', (req, res) => {
  res.status(200).send('Hello World');
});

Example

This example shows a simple Express server sending different types of responses: plain text, JSON, and setting status codes.

javascript

import express from 'express';
const app = express();
const port = 3000;

app.get('/text', (req, res) => {
  res.send('Hello from Express!');
});

app.get('/json', (req, res) => {
  res.json({ message: 'Hello JSON' });
});

app.get('/status', (req, res) => {
  res.status(404).send('Not Found');
});

app.listen(port, () => {
  console.log(`Server running on http://localhost:${port}`);
});

Output

Server running on http://localhost:3000

When visiting /text: Displays 'Hello from Express!'
When visiting /json: Displays JSON {"message":"Hello JSON"}
When visiting /status: Displays 'Not Found' with 404 status

Common Pitfalls

Common mistakes when sending responses in Express include:

• Calling res.send() or res.json() multiple times in one request, which causes errors.
• Not ending the response, leading to the client waiting indefinitely.
• Forgetting to set status codes when needed.

Always ensure only one response method is called per request.

javascript

app.get('/wrong', (req, res) => {
  // Wrong: sending twice
  res.send('First response');
  res.send('Second response'); // This will cause an error
});

app.get('/right', (req, res) => {
  res.status(200).send('Only one response');
});

Quick Reference

Method	Purpose	Example
res.send(body)	Send string, buffer, or object as response	res.send('Hello')
res.json(object)	Send JSON response with headers	res.json({ key: 'value' })
res.status(code)	Set HTTP status code	res.status(404).send('Not Found')
res.end()	End response without data	res.end()

Key Takeaways

Use res.send() or res.json() to send responses and end them automatically.

Set HTTP status codes with res.status() before sending the response.

Never call multiple response methods in the same request handler.

res.json() automatically sets the Content-Type to application/json.

Always ensure your response ends to avoid hanging requests.