This document provides an overview of design patterns in Node.js. It discusses what design patterns are, why they are useful, and examples of common creational, structural and behavioral design patterns including Singleton, Prototype, Factory Method, Builder, Chain of Responsibility, Command, Iterator, Observer and Strategy patterns. Real-world examples are provided for each pattern to illustrate how it can solve common programming problems. The document also outlines topics for future talks on additional design patterns and resources for further learning.

1. NodeJS : Design Patterns
27 Feb 2021

2. Acknowledgements
• Organising team
• O.P. Pachoriya & Sanny Kumar from Talentica.
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3. Agenda
• What are design patterns?
• Creational design patterns
• Singleton Pattern
• Prototype Pattern
• Factory Method Pattern
• Builder Pattern
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4. Agenda contd.
• Behavioural design patterns
• The chain of responsibility pattern
• The command pattern
• The iterator pattern
• The observer pattern
• The strategy pattern
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5. What should you know
• Understanding of JavaScript
• Some working knowledge with Node.js
• Experience working in Object Oriented
Programming environment
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6. Procedural Programming
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f() x
x
f()
Program
f()
f()
f()
f()
f()
f()
f()
f()

7. OOP (A brush up)
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f() x
f() x
Properties
Methods
Object

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9. OOP Benefits
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• Encapsulation: Helps reduce complexity & promotes reusability
• Abstraction: Reduces complexity & isolates impact of changes
• Inheritance: Eliminates redundant code
• Polymorphism: Promotes refactoring of long if/else, switch/case
statements

10. What are design patterns?
Reusable, reliable solutions to problem that we face
every day in software development
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11. Why Design Patterns?
• Cataloged solutions
• Reusable in many different situations
• Well documented
• Language for collaboration
• Improve architecture
• Write better program
• Become a better programmer
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12. Gang of Four (GoF)
• Elements of Reusable Object-Oriented Software
- Gang of Four, 1994
• Design Patterns definition
• Pattern name
• The problem
• The solution
• Consequences
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13. Classical design patterns
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Creational
These patterns have to do with
class instantiation, the creation of
object instances in our applications
Structural
Structural design patterns have to
do with the way objects are
composed or put together
Behavioral
Behavioral design patterns define
how objects interact with one
another

14. Other patterns
• Module
• Callback
• Middleware
• Reactor
• Blockchain
• Scheduler
• Publisher Subscriber
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15. Singleton Pattern
Ensure a class only has one instance and provide a
global point of access to it
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16. Demo - Singleton
• Singleton Problem
• Class instantiates multiple objects
• Singleton Pattern solution
• Create single instance of the class throughout execution
• Singletons in node.js
• Module caching mechanism
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17. Prototype Pattern
Specify the kinds of objects to create using
prototypical instance and create new objects by
copying this prototype
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18. Demo - Prototype
• Prototype Problem
• Object creation is repetitive and costly
• Prototype Pattern solution
• The Clone() method
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19. Factory Method Pattern
Define an interface for creating an object, but let
subclasses decide which class to instantiate. Factory
method lets a class defer instantiation to subclasses
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20. Demo - Factory Method
• Factory Method problem
• Object creation with exposed logic
• Factory Method pattern solution
• Provide common interface to create new objects
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21. Builder pattern
Separate the construction of a complex object from
its representation so that the same construction
process can create different representations
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22. Demo - Builder
• Builder Problem
• Telescoping Constructor Anti Pattern
• Builder pattern solution
• Reduce parameters to the properties, make highly
readable method calls
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23. Chain of responsibility
The GoF defines the intent of the Chain of Responsibility pattern as, to avoid
coupling the sender of a request and its receiver by giving more than one object a
chance to handle the request. Chain the receiving objects and pass the request
along the chain until an object handles it.
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24. Examples?
• People
• Assembly line
• Customer service calls
• Programming
• Express middleware
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30. The command pattern
The Gang of Four defines the intent the command pattern as encapsulating a
request as an object, thereby letting you parameterize clients with different
requests, queue or log requests, and support undoable operations
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31. Examples?
• People
• A customer in a restaurant
• Programming
• An editor application
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36. The iterator pattern
The Gang of Four defines the intent of the iterator as providing a way to access
the elements of an aggregate object (Stack, trees etc.,) sequentially without
exposing its underlying representation.
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37. Examples?
• People
• A tourist without/with guides
• Programming
• Traversing in different ways on a given collection
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41. The Observer pattern
The Gang of Four defines the intent of the observer pattern as, "Defining a one-
to-many dependency between objects so that when one object changes state, all
of its dependents are notified and updated automatically."
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42. Examples?
• People
• Newsletters
• Programming
• Event based triggers, On successful transaction,
generate receipt, send payment acknowlegement email,
send receipt etc.
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47. The strategy pattern
The Gang of Four defines a strategy as a family of algorithms, encapsulate each
one, and make them interchangeable. Strategy lets the algorithm vary
independently from the clients that use it.
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48. Examples?
• People
• Travelling to a destination
• Programming
• Support for different payment services
• Support for different logging services
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52. Design patterns are cool!
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Let's learn more
about them.
Let's use them. And let's introduce
the new ones!

53. Topics for later talks
• Structural design patterns
• Adapter patterns
• Proxy patterns
• Composite patterns
• Decorator patterns
• Other design patterns
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54. Resources
• A course by Alex Banks on LinkedIn Learning
• A course by Sachin Bhatnagar on Udemy
• https://refactoring.guru/design-patterns
• Different resourses by Mosh Hamedani
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55. Thank You
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