Enable FIFO executions processing

Defer background functions comes without a concurrency limit by default. While Defer guarantees to pick up execution by their creation order, it cannot guarantee strict sequential processing when concurrency is enabled.

Processing executions in sequence is a requirement for multiple scenarios:

• Processing certain webhooks (e.g., Shopify webhooks)
• Processing tracking events (e.g., Hubspot events)
• Dealing with strict 3rd party rate limiting.

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How to enable the FIFO mode

To enable FIFO processing, set concurrency to 1 as follows:

import { defer } from "@defer.run/client";

const importContacts = () => {
  // ...
};
export default defer(importContacts, {
  concurrency: 1,
});