30. How do you reuse information across service worker restarts?

To persist information across service worker restarts, you need to store the data in a persistent storage solution because service workers have a short lifespan and can be terminated at any time by the browser.

Options for Persisting Data Across Service Worker Restarts:

1. IndexedDB

• A durable, asynchronous key-value store that works well with service workers.
• You can use Dexie.js for easier IndexedDB management.

Example:

javascript
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// Open IndexedDB
const db = new Dexie("MyDatabase");
db.version(1).stores({
    cache: "key,value"
});

// Save data
async function saveData(key, value) {
    await db.cache.put({ key, value });
}

// Retrieve data
async function getData(key) {
    return await db.cache.get(key);
}

2. Cache API (For HTTP Responses)

• Ideal for caching fetch requests.
• Doesn't work well for arbitrary key-value data.

Example:

javascript
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// Store a response in cache
async function cacheResponse(request, response) {
    const cache = await caches.open("my-cache");
    await cache.put(request, response);
}

// Retrieve a response
async function getCachedResponse(request) {
    const cache = await caches.open("my-cache");
    return await cache.match(request);
}

3. Persistent Storage API

• Ensures storage is not cleared automatically by the browser.
• Works alongside IndexedDB or Cache API.

Example:

javascript
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navigator.storage.persist().then((granted) => {
    console.log(granted ? "Storage is persistent" : "Storage is not persistent");
});

4. SharedWorker (Limited Use)

• Can be used for communication between service workers and web pages.
• Not universally supported.

Example:

javascript
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const worker = new SharedWorker("shared-worker.js");
worker.port.postMessage({ type: "save", data: "Some data" });

Choosing the Best Approach:

• Use IndexedDB for structured, persistent data storage.
• Use Cache API for caching network requests.
• Use Persistent Storage API to prevent automatic data deletion.

Would you like an example specific to your use case?