1. JavaScript Design Patterns

2. Agenda
●
What ?
●
Types of Design Patterns
●
Some comman Anti-Patterns
●
Benefits and Disadvantages
●
Various Design Patterns

3. ●
Design pattern are recurring solutions to software design
problems you find again and again in real-world application
development
●
Standardized solutions to common problems in software
design
What ?

4. Describes a bad solution to a particular problem which resulted in a bad
situation occurring
Examples of anti-patterns in JavaScript are the following:
 Polluting the global namespace by defining a large number of variables in
the global context
 Passing strings rather than functions to either setTimeout or setInterval as
this triggers the use of eval() internally.
 Modifying the Object class prototype (this is a particularly bad anti-pattern)
 Using JavaScript in an inline form as this is inflexible
 The use of document.write where native DOM alternatives such as
document.createElement are more appropriate.
Anti-Patterns

5. Benefits & Drawbacks
Benefits:
Design patterns enable large-scale reuse of software architectures
Patterns explicitly capture expert knowledge and design tradeoffs, and make
this expertise more widely available
Patterns help improve developer communication
Drawbacks:
Patterns do not lead to direct code reuse
Patterns are deceptively simple
Teams may suffer from pattern overload
Patterns are validated by experience and discussion rather than by automated
testing

6. Types of Pattern

7. Creational Patterns
concern the process of object creation.
Structural Patterns
concern with integration and composition of classes and objects.
Behavioral Patterns
concern with class or object communication.

8. CREATIONAL
PATTERNS
Factory Method
Abstract Factory
Builder
Prototype
Singleton
STRUCTURAL
PATTERNS
Adapter
Bridge
Composite
Decorator
Façade
Flyweight
Proxy
BEHAVIORAL
PATTERNS
Chain of Responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
Strategy
Template Method
Visitor

9. Modern Day Patterns
 The Module Pattern
 The Revealing Module Pattern
 The Singleton Pattern
 The Observer Pattern
 The Mediator Pattern
 The Prototype Pattern
 The Facade Pattern
 The Factory Pattern

10. Module Design Pattern
Focuses on public and private access to methods & variables.

11. Demo

12. Advantages
Cleaner approach for developers
Supports private data
Less clutter in the global namespace
Localization of functions and variables through closures

13. Disadvantages
Private methods are unaccessible, some people say that this leads
to the inability of unit testing
Private methods and functions lose extendability since they are
unaccessible (see my comment in the previous bullet point).

14. Revealing Module Design Pattern
Same as Module Pattern, the only difference is that it was
engineered as a way to ensure that all methods and variables are
kept private until they are explicitly exposed; usually through an
object literal returned by the closure from which it’s defined.

15. Demo

16. Advantages
Cleaner approach for developers
Supports private data
Less clutter in the global namespace
Localization of functions and variables through closures
The syntax of our scripts are even more consistent
Explicitly defined public methods and variables which lead to increased
readability

17. Disadvantages
Same as Module Pattern

18. Singleton Design Pattern
Restricts instantiation of an object to a single reference

19. Demo

20. Advantages
Reduced memory footprint
Single point of access
Delayed initialization that prevents instantiation until required

21. Disadvantages
Once instantiated, they’re hardly ever “reset”.
Harder to unit test and sometimes introduces hidden dependencies.

22. Prototype Design Pattern

23. Prototype Design Pattern
The prototype pattern focuses on creating an object that can be used as a
blueprint for other objects through prototypal inheritance.

24. Demo

25. Advantages
New objects created from the “skeleton” of an existing object inherit references
to existing functions on the prototype chain, thus boosting performance and
keeping memory footprints to a minimum.
Great for an application where the focus is on object creation

26. Disadvantages
Overkill for a project that uses very few objects and/or does not have an
underlying emphasis on the extension of prototype chains

27. Factory Design Pattern
Provides an interface for developers to create new objects through
the use of the factory rather than invoking the new operator on an
object.

28. Demo

29. Advantages
The Factory pattern can be especially useful when applied to the following
situations:
 When your object's setup requires a high level of complexity
 When you need to generate different instances depending on the
environment
 When you're working with many small objects that share the same
properties or need to create components that require similar instantiation
or methods
 Great for decoupling components.

30. Disadvantages
Add an unnecessarily additional aspect of complexity to code.
Unit testing can be difficult as a direct result of the object creation process
being hidden by the factory methods.

31. Facade Design Pattern
Conceal the underlying complexity of the code by using an anonymous
function as an extra layer.
Extremely interesting and very useful for adding an extra layer of security to
your already minified code.
Extremely useful when coupled with the revealing module pattern.

32. Demo

33. Advantages
Enhances security for your web application
Works well in combination with other patterns
Easy to implement
Makes it easy to patch internals
Provides a simpler public interface
Proven useful for other major libraries such as jQuery

34. Disadvantages
One possible note worth mentioning is that a developer must decide whether the implicit
cost of implementation is really worth the abstraction (though this is generally a small
footprint).

35. Observer Design Pattern
This pattern implements a single object (the subject) that maintains a
reference to a collection of objects (known as “observers”) and broadcasts
notifications when a change to state occurs.

36. Demo

37. Advantages
Requires deeper-level thinking of the relationship between the various
components of an application
Helps us pinpoint dependencies
Excellent at decoupling objects which often promotes smaller, reusable
components
Dynamic relationships may exist between publishers and subscribers when
using this pattern. This provides a great deal of flexibility which may not be as
easy to implement when disparate parts of your application are tightly coupled.

38. Disadvantages
Checking the integrity of your application can become difficult.
Switching a subscriber from one publisher to another can be costly.

39. For reference
http://carldanley.com/javascript-design-patterns/
http://addyosmani.com/resources/essentialjsdesignpatterns/book

40. Questions ?