How to automatically clear chrome.storage

Question

My Chrome extension stores some data using chrome.storage, & fetches the results from the storage as needed.

However, I realize now that I need to periodically need to refresh the data in chrome.storage - which means clearing it from time to time.

Is it possible to:

1. Have Chrome treat chrome.storage as Session storage - that is - it clears the data once the browser closes?

2. If above is not possible, is chrome.storage.remove the only way to clear storage?

3. What happens when the chrome.storage space hits its limit?

Answer 1

1. Store Date.now() value with each object or alongside using a prefixed/suffixed key.
   A separate key might be better if the objects are big.

   • Periodically check all items and remove the expired ones i.e. where the stored date is less than current Date.now() - CACHE_DURATION_IN_MS
   • Check the expiry date when reading, and re-fetch from the web (or elsewhere) if needed

2. remove() and clear() are the only methods to delete from chrome.storage

3. 5,242,880 bytes: the maximum amount (in bytes) of data that can be stored in local storage, as measured by the JSON stringification of every value plus every key's length. This value will be ignored if the extension has the unlimitedStorage permission. Updates that would cause this limit to be exceeded fail immediately and set runtime.lastError.

   Note: chrome.runtime.lastError is undefined when no error occurred.

4. As you can see above, to ignore the default 5MB limit use "unlimitedStorage" permission.

Primitive example (a better one would use Promise):

function save(data, callback, retrying) {
    Object.keys(data).forEach(k => data[k].savedOn = Date.now());
    chrome.storage.local.set(data, () => {
        if (!chrome.runtime.lastError)
            return callback();
        if (retrying)
            throw chrome.runtime.lastError.message;
        cleanup(() => save(data, callback, true));
    });
}

const CACHE_DURATION = 7 * 24 * 3600 * 1000; // 7 days

function cleanup(callback) {
    var cutoff = Date.now() - CACHE_DURATION;
    chrome.storage.local.get(null, all => {
        var expiredKeys = Object.keys(all).filter(k => all[k].savedOn < cutoff);
        chrome.storage.local.remove(expiredKeys, callback);
    });
}