nibelung
v0.5.0
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Caching library backed by browser local storage.
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Nibelung
A library for caching things locally in websites or mobile apps.
Adds the following features to HTML localStorage and sessionStorage
- Time-to-live (TTL).
- Namespacing.
- The ability to cap the number of records (uses an LRU strategy).
- A simpler event API.
- Basic version change detection.
Creating a Hoard:
You can create a name-spaced cache as follows:
var myCache = new nibelung.Hoard({ namespace: 'fooCache' });
The following options are supported:
{
// Used to disambiguate records belonging to different cache instances.
namespace: 'my-cache-name',
// Default: false. If true, data persists across browser sessions. If false,
// data is discarded when the browser is closed.
persistent: true,
// If set to a positive integer, records will be retained for that number of
// milliseconds only. Otherwise, records will be retained indefinitely.
ttlMilliseconds: 3600000, // One hour.
// If set to a positive integer, the number of cache records will be capped
// at that number. Records will be dropped using a least-recently-used
// strategy based on last write time. If omitted, no cap will be enforced.
maxRecords: 100,
// Used to generate timestamps for records. Can be any object with a .now()
// function that returns strings strictly ordered in time. If omitted,
// Date.now() is used instead.
clock: { now: function () { ... } }
// Used to protect event handlers against reentrancy. Reentrancy can happen
// when an event handler makes changes to the cache, resulting in more events
// happening within the callstack of the first event. Can be any object with
// a .protect() function that executes its argument. If omitted,
// window.setTimeout(handler, 0) is used instead.
reentrancyProtector: { protect: function (fn) { ... } }
// Used to log warnings and errors that happen within the library. Can be
// any function that accepts a string argument. If omitted, no logs will be
// generated.
logger: function (message) { ... }
// Most useful with persistent === true. Checks the given version string
// against the current format of any previously saved records. If they don't
// match, the versionChangeHandler.onVersionChange() will be called.
version: '1',
// Most useful with persistent === true. If the given version differs from
// the version of previously-saved data, onVersionChange will be called with
// the new and old versions respectively. Returning true from
// onVersionChange will cause the Hoard to be stamped with the new version;
// returning false leaves it unchanged. This gives you the ability to
// react to version changes and handle them (e.g. by clearing the cache, or
// upgrading existing records to the new schema).
//
// As a convenience, we also provide nibelung.ClearingVersionChangeHandler in
// case you want to 'upgrade' by just deleting old data.
versionChangeHandler: { onVersionChange: function (expectedVersion, actualVersion )}
}
Basic Operations:
Adding, fetching, and removing a single value is straightforward:
myCache.putOne('1', { id: 1, foo: 'bar'});
var myFoo = myCache.getOne('1');
myCache.deleteOne('1');
Batch Operations:
You can also use batch versions of these operations:
// Adds a bunch of objects as records, using the id property as the cache
// key.
myCache.put([
{ id: 1, foo: 'bar'},
{ id: 2, foo: 'baaaar', quux: 'foo'}],
'id');
// Gets all objects matching the given keys, in the same order.
// Returns undefined
var myStuff = myCache.get([1, 2]);
// Deletes values for keys 1 and 2, ignored key 3.
myCache.remove([1, 2, 3]);
Events:
A Hoard
instance can notify you about changes to its data. Use the on
and
off
methods to register event handlers.
var myHandler = function(key, value) {
console.log(key + 'was added with value ' + value);
}
// Start listening for events on this cache.
myCache.on('PUT', myHandler);
// Stop listenting for events on this cache.
myCache.off('PUT', myHandler);
The following events are supported:
PUT
- fired when a value is added or updated.REMOVE
- fired when a value is explicitly removed, or discarded by the LRU or TTL logic.CLEAR
- fired when the hoard is cleared. Note thatclear()
will not also fire individualREMOVE
events for each record.