Learn VERCEL-SERVERLESS with Real Code Examples

Updated Nov 25, 2025

Introduction & Fundamentals Setup & Configuration Architecture & Deep Internals Performance & Security Development Workflow Learning & Career Growth Business & Strategy Examples

Code Sample Descriptions

Simple Vercel Serverless Function (JavaScript)

# vercel/demo/hello.js
export default function handler(req, res) {
    res.status(200).send('Hello, Vercel!');
}

A simple Vercel Serverless Function that responds with 'Hello, Vercel!' to HTTP requests.

Let’s Try →

Vercel Serverless Function with JSON Response

# vercel/demo/json.js
export default function handler(req, res) {
    res.status(200).json({ message: 'Hello JSON!' });
}

A function returning JSON data.

Let’s Try →

Vercel Function with Query Parameters

# vercel/demo/query.js
export default function handler(req, res) {
    const name = req.query.name || 'Guest';
    res.status(200).send('Hello, ' + name);
}

A function that reads query parameters and responds accordingly.

Let’s Try →

Vercel Function Handling POST Request

# vercel/demo/post.js
export default function handler(req, res) {
    if (req.method === 'POST') {
        const data = req.body;
        res.status(200).json({ received: data });
    } else {
        res.status(405).send('Method Not Allowed');
    }
}

A function that handles POST requests with JSON payload.

Let’s Try →

Vercel Function with Environment Variables

# vercel/demo/env.js
export default function handler(req, res) {
    const apiKey = process.env.MY_API_KEY;
    res.status(200).send('API Key length: ' + apiKey.length);
}

A function using environment variables from Vercel.

Let’s Try →

Vercel Function Redirect

# vercel/demo/redirect.js
export default function handler(req, res) {
    res.writeHead(302, { Location: 'https://example.com' });
    res.end();
}

A function that redirects requests to another URL.

Let’s Try →

Vercel Function with Custom Headers

# vercel/demo/headers.js
export default function handler(req, res) {
    res.setHeader('X-Custom-Header', 'VercelFunction');
    res.status(200).send('Custom headers added');
}

A function that adds custom headers to the response.

Let’s Try →

Vercel Function Fetching External API

# vercel/demo/fetch.js
export default async function handler(req, res) {
    const response = await fetch('https://api.github.com');
    const data = await response.json();
    res.status(200).json(data);
}

A function fetching data from an external API and returning it.

Let’s Try →

Vercel Function Serving HTML

# vercel/demo/html.js
export default function handler(req, res) {
    const html = '<!DOCTYPE html><html><body><h1>Hello HTML!</h1></body></html>';
    res.setHeader('Content-Type', 'text/html');
    res.status(200).send(html);
}

A function that responds with a simple HTML page.

Let’s Try →

Vercel Function Conditional Response

# vercel/demo/method.js
export default function handler(req, res) {
    if (req.method === 'POST') {
        res.status(200).send('You sent a POST request');
    } else {
        res.status(200).send('You sent a GET request');
    }
}

A function that responds differently based on the HTTP method.

Let’s Try →

Code Sample Descriptions

Simple Vercel Serverless Function (JavaScript)

# vercel/demo/hello.js
export default function handler(req, res) {
    res.status(200).send('Hello, Vercel!');
}

A simple Vercel Serverless Function that responds with 'Hello, Vercel!' to HTTP requests.

Let’s Try →

Vercel Serverless Function with JSON Response

# vercel/demo/json.js
export default function handler(req, res) {
    res.status(200).json({ message: 'Hello JSON!' });
}

A function returning JSON data.

Let’s Try →

Vercel Function with Query Parameters

# vercel/demo/query.js
export default function handler(req, res) {
    const name = req.query.name || 'Guest';
    res.status(200).send('Hello, ' + name);
}

A function that reads query parameters and responds accordingly.

Let’s Try →

Vercel Function Handling POST Request

# vercel/demo/post.js
export default function handler(req, res) {
    if (req.method === 'POST') {
        const data = req.body;
        res.status(200).json({ received: data });
    } else {
        res.status(405).send('Method Not Allowed');
    }
}

A function that handles POST requests with JSON payload.

Let’s Try →

Vercel Function with Environment Variables

# vercel/demo/env.js
export default function handler(req, res) {
    const apiKey = process.env.MY_API_KEY;
    res.status(200).send('API Key length: ' + apiKey.length);
}

A function using environment variables from Vercel.

Let’s Try →

Vercel Function Redirect

# vercel/demo/redirect.js
export default function handler(req, res) {
    res.writeHead(302, { Location: 'https://example.com' });
    res.end();
}

A function that redirects requests to another URL.

Let’s Try →

Vercel Function with Custom Headers

# vercel/demo/headers.js
export default function handler(req, res) {
    res.setHeader('X-Custom-Header', 'VercelFunction');
    res.status(200).send('Custom headers added');
}

A function that adds custom headers to the response.

Let’s Try →

Vercel Function Fetching External API

# vercel/demo/fetch.js
export default async function handler(req, res) {
    const response = await fetch('https://api.github.com');
    const data = await response.json();
    res.status(200).json(data);
}

A function fetching data from an external API and returning it.

Let’s Try →

Vercel Function Serving HTML

# vercel/demo/html.js
export default function handler(req, res) {
    const html = '<!DOCTYPE html><html><body><h1>Hello HTML!</h1></body></html>';
    res.setHeader('Content-Type', 'text/html');
    res.status(200).send(html);
}

A function that responds with a simple HTML page.

Let’s Try →

Vercel Function Conditional Response

# vercel/demo/method.js
export default function handler(req, res) {
    if (req.method === 'POST') {
        res.status(200).send('You sent a POST request');
    } else {
        res.status(200).send('You sent a GET request');
    }
}

A function that responds differently based on the HTTP method.

Let’s Try →