javascript-patterns

What is a pattern?

Design patterns are commonly used solutions to common software development problems.

Anti-pattern

Like changing the Object prototype is an anti-pattern. It will affect all the object in your code

Categories

1. Creational design patterns

• • This patterns deal with object creation on a more optimized way than the basic object creation.

2. Structural design patterns

• • These patterns work with relations between objects. They guarantee that if a system’s part change, nothing else has to change with it.

3. Behavioral design patterns

• • This kind of pattern acknowledge, implement and improve communication between objects of the system.

4. Concurrency design patterns

• • When you are dealing with multi threading programming these are the patterns that you will want to use.

5. Architectural design patterns

• • Design patterns that are used on the system’s architecture, like MVC or MVVM.

Creational

1. Constructor

• • allows to create objects using Classes with constructors
• • also can be created using constructor functions
• • make use of the prototype property to add the methods to be shared among all object instances

2. Module

• • makes use of closures to encapsulate the private and public properties
• • only a public API is returned, keeping everything else within the closure private.
• • utilizes an immediately-invoked function expression where object is returned
• • makes use of import and export to use the public keys in different modules
• • The greatest utility of this pattern is to make a clear separation between the public and private parts of an object.

3. Singleton

• • when we need only one instanse like a DB connection

4. Prototype

• • useful way to share properties among many objects of the same type
• • Instead of creating a duplicate of the property each time, we can simply add the property to the prototype, since all instances have access to the prototype object.
• • if not found in its own prototype, it goes through the prototype chain to find the property

5. Factory

• • function that returns a new object without using new keyword
• • this function is not a constructor nor a class
• • when we want to create multiple small objects with same config
• • these objects can be modified after creation

6. Abstract Factory pattern

• • allows us to produce families of related objects without specifying concrete classes
• • like a factory of automobiles => car, truck, motorcycle can be created
• • we have a single function to be called to get a new object of any of these types
• • we use switch to match the type and return the object of that type of automobile

7. Builder Pattern

• • create objects in "steps".
• • we separate the creation of properties and methods into different entities.
• • we can create an object and apply to it only the "steps" we need, which is a more flexible approach.
• • all the objects may not have all the functions attached to them

Structural

1. Adapter

• • allows two objects with incompatible interfaces to interact with each other.
• • Example:- XML response from one API needs to be sent to API that consumes JSON, we need to adapt the XML to JSON first

2. Decorator

• • lets you attach new behaviors to objects by placing them inside wrapper objects that contain the behaviors.
• • Like HOCs in React.js

3. Facade

• • provides a simplified interface to a library, a framework, or any other complex set of classes.
• • like React, or MUI , or map, reduce, filter functions which use for loop under the hood.

4. Proxy

• • pattern provides a substitute or placeholder for another object.
• • The idea is to control access to the original object, performing some kind of action before or after the request gets to the actual original object.
• • example -> middlewears, ExpressJs is used to build node js APIs

Behavioural

1. Chain of Responsibility

• • passes requests along a chain of handlers. Each handler decides either to process the request or to pass it to the next handler in the chain.
• • render function renders the UI , another function calls and api , that data is passd to another handler to sort , and then this data is rendered on UI

2. Iterator Pattern

• • used to traverse elements of a collection
• • for, forEach, for...of, for...in, map, reduce, filter, and so on
• • an iterator can be a function that return two functions => hasNext() and next()

3. Observer Pattern

• • lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
• • useEffect can be good example

How Pub Sub is different from Observer?

1. Observer
   • Synchronous
   • Tightly coupled - subject knows the observers observing its state
2. PubSub
   • Asynchronous behaviour
   • Pub and Sub are loosly coupled - they both are not aware about each others existance also