Client identification
Inspect the User-Agent sent by a client.
Express.js · Module
req.get
Retrieves the value of an HTTP request header by name. Use it inside a route or middleware callback to inspect client-supplied request metadata.
How it works
req.get() retrieves the value of a named HTTP request header. Header-name matching is case-insensitive, and the method returns the header value when present or undefined when absent.
Syntax
req.get(field)Parameters
| Name | Type | Description |
|---|---|---|
header | string | The name of the HTTP request header to retrieve. |
Returns
The value of the requested header, or undefined when the header is not present.
Key points
- The request object exposes request metadata, including headers that
req.get()can inspect. req.get()is one of the request methods available for working with incoming HTTP requests.- Call the method on the request object supplied to a route or middleware callback.
Common mistakes
reqincludes Node’s built-in request capabilities, so usereq.get()specifically when you want Express’s header lookup helper.
Example: Read a request header
const express = require('express');
const app = express();
app.get('/profile', (req, res) => {
const userAgent = req.get('User-Agent');
res.json({ userAgent });
});
app.listen(3000);Reads the request's User-Agent header and returns it as JSON.
When to use it
Content negotiation
Read an Accept or Content-Type-related request header.
Custom request metadata
Use a custom header to apply request-specific logic.
Related
reqreq.headersreq.headerapp.getrouter.get