Plaid API Integration

Integrate Plaid for connecting bank accounts and syncing transactions in TypeScript applications using Bun.

Installation

bun add plaid

Client Initialization

import { Configuration, PlaidApi, PlaidEnvironments } from 'plaid';

const plaidClient = new PlaidApi(new Configuration({
  basePath: PlaidEnvironments[process.env.PLAID_ENV || 'sandbox'],
  baseOptions: {
    headers: {
      'PLAID-CLIENT-ID': process.env.PLAID_CLIENT_ID,
      'PLAID-SECRET': process.env.PLAID_SECRET,
    }
  }
}));

Link Token Creation

Omit redirect_uri to use popup mode — required for local HTTP development:

const response = await plaidClient.linkTokenCreate({
  user: { client_user_id: `user-${Date.now()}` },
  client_name: 'My App',
  products: ['transactions'],
  country_codes: ['US'],
  language: 'en',
  // No redirect_uri = popup mode, works with HTTP localhost
});
const linkToken = response.data.link_token;

Token Exchange

After the user completes Link, exchange the temporary public_token for a permanent access_token:

const response = await plaidClient.itemPublicTokenExchange({ public_token });
const { access_token, item_id } = response.data;
// Store access_token securely — never expose to clients

Transaction Sync

Plaid returns a maximum of 500 transactions per request. Always paginate:

let offset = 0;
const count = 500;

while (true) {
  const response = await plaidClient.transactionsGet({
    access_token,
    start_date: '2023-01-01',
    end_date: '2024-12-31',
    options: { count, offset },
  });

  // Process response.data.transactions
  offset += response.data.transactions.length;
  if (offset >= response.data.total_transactions) break;
}

For ongoing incremental updates, prefer transactionsSync with a cursor — see references/api-reference.md.

Error Handling

Catch Plaid errors from error.response?.data:

try {
  await plaidClient.transactionsGet({ ... });
} catch (error: any) {
  const plaidError = error.response?.data;
  if (!plaidError) throw error;

  switch (plaidError.error_code) {
    case 'ITEM_LOGIN_REQUIRED':
      // Re-initialize Link in update mode
      break;
    case 'INVALID_ACCESS_TOKEN':
      // Token revoked — delete item, prompt re-link
      break;
    case 'PRODUCT_NOT_READY':
      // Data still processing — retry after delay
      break;
    default:
      throw new Error(`Plaid error: ${plaidError.error_code} — ${plaidError.error_message}`);
  }
}

Database Setup

Use Bun SQLite with items → accounts → transactions hierarchy. For the complete schema with indexes, prepared statements, and TypeScript types, see references/code-examples.md.

Reference Files

• references/code-examples.md — Full working implementations: bank connection flow with Elysia server, transaction sync with pagination, complete Bun SQLite database module, CLI integration
• references/api-reference.md — All API endpoints with request/response shapes, sandbox test credentials, webhook events, rate limits