What are Webhooks?

What You'll Learn

What webhooks are
Webhooks vs polling
Implementation example

Webhooks are HTTP callbacks that notify your server when events occur in another system.

Webhooks vs Polling

Aspect	Polling	Webhooks
Direction	Client → Server	Server → Client
Efficiency	Wastes resources	Event-driven
Real-time	Delayed	Immediate
Complexity	Simple	More setup

How Webhooks Work

code.jsJavaScript

1. Register webhook URL with provider
2. Event occurs (e.g., payment completed)
3. Provider sends HTTP POST to your URL
4. Your server processes the event

Implementation

code.jsJavaScript

// Receiving webhooks
app.post('/webhooks/stripe', express.raw({ type: 'application/json' }), (req, res) => {
  const sig = req.headers['stripe-signature'];

  try {
    // Verify webhook signature
    const event = stripe.webhooks.constructEvent(req.body, sig, webhookSecret);

    // Handle event
    switch (event.type) {
      case 'payment_intent.succeeded':
        handlePaymentSuccess(event.data.object);
        break;
      case 'customer.subscription.deleted':
        handleCancellation(event.data.object);
        break;
    }

    res.json({ received: true });
  } catch (err) {
    res.status(400).send(`Webhook Error: ${err.message}`);
  }
});

// Sending webhooks
async function sendWebhook(url, event, data) {
  const payload = { event, data, timestamp: Date.now() };
  const signature = createHmac('sha256', secret)
    .update(JSON.stringify(payload))
    .digest('hex');

  await fetch(url, {
    method: 'POST',
    headers: { 'X-Webhook-Signature': signature },
    body: JSON.stringify(payload),
  });
}