ClassCache

Cache a class instance by key. Creates a new instance if the key doesn't exist, otherwise returns the cached instance. Uses the prototype chain to delegate options. Optional LRU garbage collection. Built as a general base class for nanocomponent-cache.

Usage

const ClassCache = require('class-cache')
const DefaultClass = require('default-class')
const SomeClass = require('some-class')
const AnotherClass = require('another-class')
const AThirdClass = require('a-third-class')
 
const c = new ClassCache({ lru: 1000 })
 
c.register(DefaultClass, {args: ['some', {default: 'constructor-args'}]})
 
const a = c.get('my-instance') // Creates and returns an instance of DefaultClass
const b = c.get('my-instance')
console.log(a === b) // true
 
c.register({
  'some-class': SomeClass,
  'another-class': {class: AnotherClass, args: ['class', 'specific'], gc: instance => instance.coolToGC}
})
 
c.get('some-instance', 'some-class') // return new SomeClass instance
c.get('some-instance', 'some-class') // return same instance as above
c.get('some-instance', 'another-class') // Create AnotherClass instance and replace the SomeClass instance stored at 'some-instance'

• example.js

Installation

$ npm install class-cache

API

ClassCache = require('class-cache)

Import ClassCache class.

c = new ClassCache([opts])

Create a new component.

opts include:

{
  gc: (instance) => false // a default garbage collection function
  args: [] // Default args used for instantiating all classes,
  lru: 0 // Enable LRU gc by setting this to an integer greater than 0
}

c.register([typeKey = 'default'], Class, [opts])

Define a Class for the optional typeKey. The default typeKey is default, which is used whenever a typeKey is omitted during gets and sets. opts include:

{
  gc: undefined // a typeKey specific GC function,
  args: undefined // default arguments instance arguments
  // These options delegate to the top level options if left un-implemented
}

This is a shortcut for defining with a typeObject:

c.register({
  typeKey: { class: Class, ...opts }
})

c.register({ typeObject })

Define class 'type's using a typeObject definition. A typeObject is an object who's keys define the type name which are associated with a Class and optionally args and a type specific gc function.

c.register({
  default: Class, // Class with no args or gc.  Uses instance gc function.
  baz: { class: Class, ...opts }
})

Types are Object.assigned over previously registered types.

c.unregister(...types)

Pass typeKeys as arguments to un-register them. Instances are untouched during this process.

c.get(key, [Class || typeKey], [opts])

Return instance of Class or defined type class at key. If an instance does not yet exist at key, it will be instantiated with args along with a key specific gc function. If type is not defined, this method will throw.

Omitting optional method arguments delegates to the next most specific option.

c.get('some-key') // Return or create the 'default' Class
c.get('some-key', {args: ['arg0', 'arg2']})
c.get('some-key', null, {args: ['arg0', 'arg2']}) // Return the default registered class with specific args
c.get('some-key', 'some-type', { args: ['arg0', 'arg2'] }) // Return the `some-type` class at `some-key`.
c.get('some-key', SomeOtherClass, { args: ['arg0', 'arg2'], gc: instance => true })

If key is already instantiated, args is ignored. Pass changing properties as subsequent calls to the returned instance. If type or Class changes, the key instance is re-instantiated.

c.set(key, [Class || type], [opts])

Force instantiate the class instance at key. Follows the same override behavior as get. If you must change args on a key, this is the safest way to do that.

Returns the newly created instance.s

c.gc()

Run the various gc functions defined. For each key, only the most specific gc function set is run. Return true from the gc functions to garbage collect that instance, and false to preserve.

This is used to clean out instances you no longer need.

c.clear()

Clear all key instances. The gc functions for each instance will be run receiving the following signature: (instance, key, true) => {}. If your instance needs to let go of resources, watch for the second argument to equal true, indicating tht the instance will be deleted.

c.delete(key)

Delete specific key instance. Will run the gc function passing true as the second argument ((instance, key, true) => {}).

c.has(key)

Return true if key exists.

See examples for more details.

c.cache

Getter that returns a snapshot of the cache for inspection.

See Also

• nanocomponent-cache: A class-cache subclass that ships sensible defaults for nanocomponents. If you are using this with choo, you should probably use that instead.
• Choo component discussions: There are a number of ideas on how to solve this class of problems. See discusson here.

License

MIT