Design patterns

In this chapter, we will take a look at some of the design patterns that make sense for JavaScript. However, coding patterns are very specific for JavaScript and are of great interest to us. While we spend a lot of time and effort trying to understand and master design patterns, it is important to understand anti-patterns and how to avoid pitfalls. In the usual software development cycle, there are several places where bad code is introduced, mainly around the time where the code is nearing a release or when the code is handed over to a different team for maintenance. If such bad design constructs are documented as anti-patterns, they can provide guidance to developers in knowing what pitfalls to avoid and how not to subscribe to bad design patterns. Most languages have their set of anti-patterns. Based on the kind of problems that they solve, design patterns were categorized into a few broad categories by the GOF:

• Creational design patterns: These patterns deal with various mechanisms of object creation. While most languages provide basic object creation methods, these patterns look at optimized or more controlled mechanisms of object creation.
• Structural design patterns: These patterns are all about the composition of objects and relationships among them. The idea is to have minimal impact on overall object relationships when something in the system changes.
• Behavioral design patterns: These patterns focus on the interdependency and communication between objects.

The following table is a useful ready reckoner to identify categories of patterns:

• Creational patterns:
  • Factory method
  • Abstract factory
  • Builder
  • Prototype
  • Singleton
• Structural patterns:
  • Adapter
  • Bridge
  • Composite
  • Decorator
  • Fa?ade
  • Flyweight
  • Proxy
• Behavioral patterns
  • Interpreter
  • Template method
  • Chain of responsibility
  • Command
  • Iterator
  • Mediator
  • Memento
  • Observer
  • State
  • Strategy
  • Visitor

Some patterns that we will discuss in this chapter may not be part of this list as they are more specific to JavaScript or a variation of these classical patterns. Similarly, we will not discuss patterns that do not fit into JavaScript or are not in popular use.