deferq

A tiny, zero-dependency JavaScript library for queuing async actions when offline and automatically retrying them when connectivity returns.

• Lightweight: ~30 lines of code
• Zero dependencies
• Concurrent retries: All queued actions run in parallel when back online
• Flexible: Queue any async function by name

Ideal for simple offline support without the complexity of service workers.

Installation

Via npm

Install with: npm install deferq

Via CDN

<script src="https://app.unpkg.com/deferq@1.1.3/files/index.js"></script>

Usage

1. Initialize the library (once)

<script type="module">
  import { addToQueue, register } from 'https://cdn.jsdelivr.net/npm/deferq@1.1.3/index.js'; // Automatically registers the "online" listener
</script>

2. Queue actions when offline

async function createPost({ post }) {
  if (!navigator.onLine) {
    addToQueue('networkQueue', 'createPost' { post });
    showToast("Offline — we'll retry when you're back online.", 5);
    return;
  }

  const res = await fetch('/api/post', {
    method: 'POST',
    body: JSON.stringify({ post }),
    headers: { 'Content-Type': 'application/json' }
  });
  // handle response...
}

// Call your function as usual
createPost({ post: "Hello world!" });

3. Automatic retry

When the browser fires the "online" event, deferq:

• Loads the queue from internal storage.
• Executes all queued functions serially to avoid a thundering herd.
• Removes successful actions.
• Keeps persistent failures for the next online event.

No additional setup required.

API

addToQueue(key: string, fnName: string, payload: any)

Queues an action.

• key: key for the queue (e.g., 'networkQueue', 'fetchQueue', 'transferQueue')
• fnName: Name of the function as it was registered to deferq.
• payload: Data to pass to the function when replayed

Example: addToQueue('networkQueue', 'createPost', { post: 'data' })

How It Works

• When offline, use addToQueue instead of calling the function directly.
• Actions are cached in internal storage under the given key.
• On "online", deferq replays all actions serially.
• Successful actions are removed; failed ones remain for future retries.

Notes

• In v1.1.3, actions are no longer stored in localStorage to avoid pollution and XSS attacks.
• Functions to queue must be pure functions and not use global state, for safety and proper application.
• No built-in queue size limit (add your own in production if needed).
• Works in all modern browsers.

Function Naming Requirement

For automatic retry to work, the calling function must have a name that appears in the stack trace.

Works:

• Named function declarations: function createPost() {}
• Named function expressions: const post = function createPost() {}

Does not work:

• Arrow functions: const createPost = async () => {}
• Anonymous functions

Recommendation: Use named functions for actions that may be queued offline.

License

MIT