cache-service-cache-module

• A light-weight cache plugin for superagent-cache and cache-service
• AND a standalone in-memory cache that's optionally backed by localStorage and sessionStorage

Features

• Optionally backed by localStorage and sessionStorage
• Background refresh
• No external dependencies
• Robust API
• Built-in logging with a verbose flag.
• Compatible with cache-service and superagent-cache
• Excellent .mset() implementation which allows you to set expirations on a per key, per function call, and/or per cache-service-cache-module instance basis.

Basic Usage

Require and instantiate

var cModule = require('cache-service-cache-module');

var cacheModuleConfig = {storage: 'session', defaultExpiration: 60};
var cacheModule = new cModule(cacheModuleConfig);

Cache!

cacheModule.set('key', 'value');

Cache Module Configuration Options

cache-service-cache-module's constructor takes an optional config object with any number of the following properties:

type

An arbitrary identifier you can assign so you know which cache is responsible for logs and errors. IMPORTANT If you use more than one instance of cache-service-cache-module at a time and persist to browser storage from both of them, you must set this to a unique value. If you do not, your cache instances will overwrite each other when persisting to browser storage.

• type: string
• default: 'cache-module'

storage

Indicates whether cacheModule's in-memory cache should be backed by localStorage or sessionStorage. The available options are 'local' and 'session'. If not set, or if running in node, it will default to an in-memory cache. When a browser storage is activated, cacheModule will still write to and read from an in-memory cache in the interest of speed, but at initialization it will load it's in-memory cache from browser storage and write all changes back to browser storage.

• type: string
• default: ''

defaultExpiration

The expiration to include when executing cache set commands. Can be overridden via .set()'s optional expiraiton param.

• type: int
• default: 900
• measure: seconds

backgroundRefreshInterval

How frequently should all background refresh-enabled keys be scanned to determine whether they should be refreshed. For a more thorough explanation on background refresh, see the Using Background Refresh section.

• type: int
• default: 60000
• measure: milliseconds

backgroundRefreshMinTtl

The maximum ttl a scanned background refresh-enabled key can have without triggering a refresh. This number should always be greater than backgroundRefreshInterval.

• type: int
• default: 70000
• measure: milliseconds

backgroundRefreshIntervalCheck

Whether to throw an exception if backgroundRefreshInterval is greater than backgroundRefreshMinTtl. Setting this property to false is highly discouraged.

• type: boolean
• default: true

verbose

When used with cache-service, this property is overridden by cache-service's verbose value.

When false, cache-service-cache-module will log only errors. When true, cache-service-cache-module will log all activity (useful for testing and debugging).

• type: boolean
• default: false

readOnly

Whether a cache should not be written to. Useful if you're sharing a redis cache with another team and your contract with them is that you will not alter their data.

• type: boolean
• default: false

API

As a cache-service-compatible cache, cache-service-cache-module matches cache-service's API.

.get(key, callback (err, response))

Retrieve a value by a given key.

• key: type: string
• callback: type: function
• err: type: object
• response: type: string or object

.mget(keys, callback (err, response))

Retrieve the values belonging to a series of keys. If a key is not found, it will not be in response.

• keys: type: an array of strings
• callback: type: function
• err: type: object
• response: type: object, example: {key: 'value', key2: 'value2'...}

.set(key, value, [expiraiton], [refresh(key, cb)], [callback])

See the Using Background Refresh section for more about the refresh and callback params.

Set a value by a given key.

• key: type: string
• value: type: string || objects
• expiration: type: int, measure: seconds
• refresh: type: function
• callback: type: function

.mset(obj [, expiration, callback])

Set multiple values to multiple keys

• obj: type: object, example: {'key': 'value', 'key2': 'value2', 'key3': {cacheValue: 'value3', expiration: 60}}
• callback: type: function

This function exposes a heirarchy of expiration values as follows:

• The expiration property of a key that also contains a cacheValue property will override all other expirations. (This means that, if you are caching an object, the string 'cacheValue' is a reserved property name within that object.)
• If an object with both cacheValue and expiration as properties is not present, the expiration provided to the .mset() argument list will be used.
• If neither of the above is provided, each cache's defaultExpiration will be applied.

.del(keys, [callback (err, count)])

Delete a key or an array of keys and their associated values.

• keys: type: string || array of strings
• callback: type: function
• err: type: object
• count: type: int

.flush([cb])

Flush all keys and values.

• callback: type: function

Using Background Refresh

With a typical cache setup, you're left to find the perfect compromise between having a long expiration so that users don't have to suffer through the worst case load time, and a short expiration so data doesn't get stale. cache-service-cache-module eliminates the need to worry about users suffering through the longest wait time by automatically refreshing keys for you. Here's how it works:

How do I turn it on?

By default, background refresh is off. It will turn itself on the first time you pass a refresh param to .set().

Configure

There are three options you can manipulate. See the API section for more information about them.

• backgroundRefreshInterval
• backgroundRefreshMinTtl
• backgroundRefreshIntervalCheck

Use

Background refresh is exposed via the .set() command as follows:

cacheModule.set('key', 'value', 300, refresh, cb);

If you want to pass refresh, you must also pass cb because if only four params are passed, cache-service-cache-module will assume the fourth param is cb.

The Refresh Param

refresh(key, cb(err, response))

• key: type: string: this is the key that is being refreshed
• cb: type: function: you must trigger this function to pass the data that should replace the current key's value

The refresh param MUST be a function that accepts key and a callback function that accepts err and response as follows:

var refresh = function(key, cb){
  var response = goGetData();
  cb(null, response);
}