Week 1 Day 5: Mini Project - URL Shortener API

Welcome to our first Mini Project! We will build a simple version of Bit.ly.

Requirements

1. Shorten: Accept a long URL, return a short ID.
2. Redirect: Access short ID, redirect to long URL.
3. Data: Store in memory (for now).

The Stack

• Language: JavaScript (Node.js)
• Framework: Express.js
• Database: In-Memory Map (Future: Redis/Postgres)

Implementation

1. Setup

npm init -y
npm install express shortid

2. The Code (server.js)

const express = require('express');
const shortid = require('shortid');

const app = express();
app.use(express.json());

// Database (In-Memory)
const urlDatabase = {};

// 1. Shorten URL
app.post('/shorten', (req, res) => {
    const { longUrl } = req.body;
    if (!longUrl) return res.status(400).json({ error: 'longUrl required' });

    const id = shortid.generate();
    urlDatabase[id] = longUrl;

    res.json({ 
        original: longUrl, 
        short: `http://localhost:3000/${id}` 
    });
});

// 2. Redirect
app.get('/:id', (req, res) => {
    const { id } = req.params;
    const longUrl = urlDatabase[id];

    if (longUrl) {
        res.redirect(longUrl);
    } else {
        res.status(404).send('URL not found');
    }
});

app.listen(3000, () => console.log('Server running on port 3000'));

Testing

1. POST to http://localhost:3000/shorten Body: { "longUrl": "https://www.google.com" } Response: { "short": "http://localhost:3000/ad23s" }
2. GET http://localhost:3000/ad23s Result: Redirects to Google!

System Design Critique

This works for 1 user. What if we have 1 million?

• Issue: In-memory data is lost on restart.
• Fix: Use a Database (Week 3).
• Issue: Single server can’t handle load.
• Fix: Multiple servers + Load Balancer (Week 2).
• Issue: Short IDs might collide (rare, but possible).

Next week, we tackle Scalability! We will make this robust. 🚀

Next Step

Next: Vertical Vs Horizontal Scaling →