LRU Cache for Browser's Local Storage

Welcome to LocalStorageLRU, a browser LocalStorage Javascript cache.

If you are trying to use this package, check out https://www.npmjs.com/package/@sleaze/local-storage-lru.

Problem

Saving an increasing number of key/value pairs in localStorage causes it to fill up at some point. From that point on, adding/modifying throws an exception.

Solution

Keep track of last n recently accessed/modified keys. If an exception occurs, randomly remove a few keys which aren't in that list and also – optionally – only whitelisted ones. Then try again storing the new value.

Benefits

• The entire overhead is one additional key/value pair storing the pointers to these LRU keys.
• The keys and values you try to store are not modified.

Design Goals

• robust: no exceptions are thrown (only if there is a problematic key)
• universal: also supports storing objects, Date, BigInt, arrays etc..
• backwards compatible: if you already store string values, they're not modified. You can even tell it to attempt parsing existing JSON values.

Usage

This is how to instantiate the wrapper class.

Options:

• recentKey (optional): the string of the key, under which the list of recently accessed keys is stored.
• maxSize (optional): the maximum number of keys to keep in the list of recently used keys. A larger list reduces the chances of deleting an "important" key, but at the same time, overall more storage is used.
• isCandidate (optional): a function that takes a key and returns true if the key is a candidate for deletion. By default, any key except for the recentKey is a candidate. Optional second argument is the array of all recent keys.
• fallback (optional, default false): if true, localStorage is checked if it works. If not, data is stored in a mockup storage with limited space.
• serializer (optional): by default JSON.stringify, but you can use your own.
• deserializer (optional): counterpart to the above, by default JSON.parse.
• parseExistingJSON (optional): if true, it tries to deserialize already existing JSON values.
• typePrefixes (optional): prefixes to serialized values if they're not stored a strings – somehow, we have to mark values if they are a complex object...
• typePrefixDelimiter (optional): string appended to each typePrefix to separate from the serialized value – default: \0

// simple:
const storage = new LocalStorageLRU();

// with options:
function candidate(key: string): boolean {
  if (key.startsWith('preserved-')) {
    return false;
  }
  return true;
}

const storage = new LocalStorageLRU({
  recentKey: RECENTLY_KEY,
  maxSize: RECENTLY_KEEP,
  isCandidate: candidate,
  fallback: true,
});

// set/get/delete
storage.set('foo', 'bar');
storage.get('foo') == 'bar'; // true
storage.delete('foo');

// iterate
storage.set('key1', '1');
storage.set('key2', '2');
storage.set('key3', '3');
const entries: [string, any][] = [];
for (const [k, v] of storage) {
  entries.push([k, v]);
}
entries; // equals: [[ 'key1', '1' ], [ 'key2', '2' ], [ 'key3', '3' ]]

For more, check out the documentation or the tests.

Development

The setup follows this step-by-step guide.

Requirements

• node.js v18.20.2 or newer is required to build this project.

Release

There are some hooks registered, see link above, to check for clean git tree, all tests passing and linting.

npm version patch
npm publish --access public

License

Apache 2.0

Credit

LocalStorageLRU was originally forked from https://github.com/sagemathinc/local-storage-lru.