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Learning JavaScript Design Patterns

Chapter 9. JavaScript Design Patterns

Singleton Pattern

Applicability

  • There must be exactly one instance of a class, and it must be accessible to clients from a well-known access point.
  • When the sole instance should be extensible by sub-classing, and clients should be able to use an extended instance without modifying their code.

Mediator Pattern

It is an object that handles the workflow between many other objects, aggregating the responsibility of that workflow knowledge into a single object

Command Pattern

It facilitates the execution of commands between an Invoker and a Receiver by encapsulating the implementation details on a method instead of calling the instance's methods that may change in the future.

Abstract Class

An Abstract Class provides an Interface but it doesn't have instances. It acts as a base class from which others are derived.

Concrete Class

A Concrete Class is a derived class which implements the missing functionality of an Abstract class.

Facade Pattern

It hides the complexity of use of an API by providing an interface which is easier to use, hiding all the implementation details from the user.

Factory Pattern

When to use?

  • When creating objects or components is really complex
  • When we need to create different instances of objects
  • When working with a lot of small objects that share the same properties.
  • When composing objects with instances of other objects

Flyweight Pattern

The Flyweight pattern is a classical structural solution for optimizing code that is repetitive, slow and inefficiently shares data. It aims to minimize the use of memory in an application by sharing as much data as possible with related objects.

The two states of a Flyweight Pattern

Intrinsic

Intrinsic information may be required by internal methods in our objects which they absolutely cannot function without.

Extrinsic

Extrinsic information can however be removed and stored externally.

Types of Flyweight components

Flyweight

defines an interface through which flyweights are able to receive and act on existing states.

Concrete Flyweight

actually implements the Flyweight interface and stores intrinsic state. Concrete Flyweights need to be shareable and capable of manipulating state tha is extrinsic.

Flyweights Factory

manages flyweight objects and creates them too. it makes sure that our flyweights are shared and manages them as a group of objects which can be queried if we require individual instances. If an object has been already created in the group it returns it, otherwise it adds a new object to the pool and returns it.