Express.js res.locals Property

The res.locals property is an object that contains response local variables scoped to the request and because of this, it is only available to the view(s) rendered during that request/response cycle (if any). 

Syntax:

res.locals

Parameter: No parameters. 

Return Value: Object 

Installation of the express module:

You can visit the link to Install the express module. You can install this package by using this command.

npm install express

After installing the express module, you can check your express version in the command prompt using the command.

npm version express

After that, you can just create a folder and add a file, for example, index.js. To run this file you need to run the following command.

node index.js

Project Structure:

Example 1: Filename: index.js

javascript

const express = require('express');
const app = express();
const PORT = 3000;

app.get('/', function (req, res) {
    res.locals.user = 'GeeksforGeeks';
    console.log(res.locals);
    res.end();
});

app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Steps to run the program:

Make sure you have installed the express module using the following command:

npm install express

Run the index.js file using the below command:

node index.js

Output:

Console Output:

Server listening on PORT 3000

Browser Output:

Now open your browser and go to http://localhost:3000/, now you can see the following output on your console:

Server listening on PORT 3000
[Object: null prototype] { user: 'GeeksforGeeks' }

Example 2: Filename: index.js

javascript

const express = require('express');
const app = express();
const PORT = 3000;

app.get('/', function (req, res) {

    // Sending multiples locals
    res.locals.name = 'Gourav';
    res.locals.age = 13;
    res.locals.gender = 'Male'

    console.log(res.locals);
    res.end();
});

app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Steps to run the program:

Run the index.js file using the below command:

node index.js

Output: Now open your browser and make a GET request to http://localhost:3000, now you can see the following output on your console:

Server listening on PORT 3000
[Object: null prototype] { name: 'Gourav', age: 13, gender: 'Male' }

Reference: https://expressjs.com/en/4x/api.html#res.locals