cors middleware setup in Express - Mini Project: Build & Apply

CORS Middleware Setup in Express

📖 Scenario: You are building a simple Express server that will serve data to a frontend running on a different domain. To allow this, you need to set up CORS (Cross-Origin Resource Sharing) middleware.

🎯 Goal: Set up CORS middleware in an Express app to allow requests from http://example.com.

📋 What You'll Learn

Create an Express app instance called app

Import the cors package

Create a CORS options object called corsOptions that allows origin http://example.com

Use the cors middleware with the corsOptions in the Express app

💡 Why This Matters

🌍 Real World

Many web apps need to share resources between different domains safely. Setting up CORS middleware in Express helps control which domains can access your server.

💼 Career

Backend developers often configure CORS to secure APIs and enable frontend-backend communication across domains.

1

Create Express app instance

Import express and create an Express app instance called app by calling express().

Express

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

Need a hint?

Use const app = express() to create the app.

2

Import cors package and create options

Import the cors package and create a variable called corsOptions that is an object with the property origin set to 'http://example.com'.

Express

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

Need a hint?

Use const cors = require('cors') and set corsOptions with origin property.

3

Use cors middleware with options

Use the cors middleware in the Express app by calling app.use() with cors(corsOptions) as the argument.

Express

const express = require('express');
const app = express();
const cors = require('cors');
const corsOptions = { origin: 'http://example.com' };
// Your code here

Need a hint?

Call app.use(cors(corsOptions)) to apply the middleware.

4

Add a simple route and export app

Add a GET route on '/' that sends the text 'Hello World'. Then export the app using module.exports = app.

Express

const express = require('express');
const app = express();
const cors = require('cors');
const corsOptions = { origin: 'http://example.com' };
app.use(cors(corsOptions));
// Your code here

Need a hint?

Use app.get('/', (req, res) => { res.send('Hello World') }) and export the app.