Generate invoice PDFs from Stripe webhooks with Node.js

What you'll need

• An InvoiceCraftly API key (see the API reference).
• Node.js 18 or later.
• A Stripe account (test mode is fine) with a webhook endpoint configured for checkout.session.completed, and its signing secret.
• The official stripe npm package: npm install stripe.

Map the Stripe session into an invoice

This pure function has no Stripe or network dependency, so it's easy to unit test on its own before wiring it into a webhook handler:

// map-stripe-session.js
function addressLinesFrom(address) {
  const stateZip = [address.state, address.postal_code].filter(Boolean).join(' ');
  const cityLine = [address.city, stateZip].filter(Boolean).join(', ');
  return [address.line1, address.line2, cityLine, address.country].filter((line) => line && line.trim().length > 0);
}

export function mapStripeSessionToInvoiceDocument(session, { seller, number, issueDate, dueDate }) {
  const document = {
    type: 'invoice',
    number,
    issueDate,
    currency: session.currency.toUpperCase(),
    seller,
    buyer: {
      name: session.customer_details.name,
      addressLines: addressLinesFrom(session.customer_details.address)
    },
    items: session.line_items.data.map((item) => ({
      description: item.description,
      quantity: item.quantity,
      unitPrice: item.price.unit_amount / 100,
      taxRate: 0
    }))
  };
  if (dueDate) document.dueDate = dueDate;
  return document;
}

The webhook handler

// npm install stripe
import { createServer } from 'node:http';
import { mkdir, writeFile } from 'node:fs/promises';
import Stripe from 'stripe';
import { mapStripeSessionToInvoiceDocument } from './map-stripe-session.js';

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY);
const endpointSecret = process.env.STRIPE_WEBHOOK_SECRET;
const invoiceCraftlyApiKey = process.env.INVOICECRAFTLY_API_KEY;

const seller = { name: 'Your Company Name', addressLines: ['Your Company Address'] };

await mkdir('invoices', { recursive: true });

createServer(async (request, response) => {
  const chunks = [];
  for await (const chunk of request) chunks.push(chunk);
  const rawBody = Buffer.concat(chunks);

  let event;
  try {
    event = stripe.webhooks.constructEvent(rawBody, request.headers['stripe-signature'], endpointSecret);
  } catch (error) {
    response.writeHead(400);
    return response.end(`Webhook signature verification failed: ${error.message}`);
  }

  if (event.type === 'checkout.session.completed') {
    const session = await stripe.checkout.sessions.retrieve(event.data.object.id, { expand: ['line_items'] });
    const invoice = mapStripeSessionToInvoiceDocument(session, {
      seller,
      number: session.id,
      issueDate: new Date().toISOString().slice(0, 10)
    });

    const pdfResponse = await fetch('https://invoicecraftly.com/api/v1/documents/pdf', {
      method: 'POST',
      headers: { Authorization: `Bearer ${invoiceCraftlyApiKey}`, 'Content-Type': 'application/json' },
      body: JSON.stringify(invoice)
    });

    if (pdfResponse.ok) {
      const pdfBuffer = Buffer.from(await pdfResponse.arrayBuffer());
      await writeFile(`invoices/${session.id}.pdf`, pdfBuffer);
    } else {
      console.error(`InvoiceCraftly render failed: ${pdfResponse.status}`);
    }
  }

  response.writeHead(200);
  response.end('ok');
}).listen(3000);

Checkout Sessions don't include line items in the webhook payload — line_items is an expandable field, so event.data.object.line_items is undefined. Retrieving the session with expand: ['line_items'] is what populates them, and it's the most common gotcha when wiring Stripe Checkout to any downstream system, not just this one.

One currency caveat before you go live: for zero-decimal currencies (JPY, KRW, VND and friends) Stripe's unit_amount is already in whole units, so the mapper's unit_amount / 100 is only correct for standard two-decimal currencies like USD or EUR.