Design Patterns

Updated: October 15, 2024

Design Patterns are in every language. Some patterns pertain particularly to a specific language.

Design patterns are typical solutions to common problems. These problems can exist because a language may be missing a level of abstraction. For example JS does not have Range but can be created with
an iterator pattern.

References:
Fireship
refactoring.guru

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Table of Contents

• Creational
• Patterns
• Types

Must know

Lets says window is an object, an instance.
It could have METHODS open and close, defined in a class.
Then it could have a state to track if it is open or closed, this would be a property.

CREATIONAL

Provide object creation mechanisms that increase flexibility and reuse of existing code.

Factory Method

• Instead of conditional checking create subclass from a superclass.
• Rather than use keyword to instantiate an object use a function or method to do it.
• Objects returned from the factory method are referred to as products.
• Subclasses can alter the class of objects being returned by the factory method.
• Can return existing objects from a cache, an object pool, or another source.
• Use the Factory Method when you want to save system resources by reusing existing objects instead of rebuilding them each time.

Abstract Factory

Prototype (clone, think inheritance class)

• Instead of inheriting functionality from a class, inherite from an object already created.

Builder

• Create object step-by-step using methods rather than a constructor.

Singleton

• Object that can only be instantiated once.
• Typical use case is in global settings.

STRUCTURAL

Explain how to assemble objects and classes into larger structures, while keeping these structures flexible and efficient.

Facade

• Like a simple API that hides low level details user does not need to know about.
• Like how jQuery is a facade for Javascript.

Proxy (substitute)

• Used to be able to manipulate an object.
• Ability to intercept data and update UI when data changes.

BEHAVIORAL

Take care of effective communication and the assignment of responsibilities between objects.

Iterator

• Allows to traverse through a collection of objects.
• For Loop and Range are an abstractions of the iterator pattern.
• Is a pull based system.

Observer

• Is a push based system.
• Allows many objects to subscribe to events that are broadcast by another object.
• One to Many relationship. Like a radio signal from a tower.
• Like && Subscribe is an example of this pattern.

Mediator

• Used to handle Many-to-Many relationships.
• Like middleware that provides separation of concerns for requests being sent for a response. (place in proper format)

State

• An object behaves differently based on a finite number of states.
• Used in place of case, switch or other conditional statements.
• Start with a base class and then provide it different funtinionality based on its internal state.

Strategy

• Lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.