designpatterns-singleton-facade.md

Design Patterns

^A design pattern is a way to solve a code problem in a way that is recognizable and reusable. It gives us common language with which to discuss code techniques.

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Objectives

• Explain what the Singleton pattern is
• Explain two reasons to use this pattern
• Review two ways to use the Singleton pattern
• Explain what the Facade pattern is
• Explain two reasons to use this pattern

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#[fit] The Singleton Pattern

Make One

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Singleton: What is it?

• A Singleton is a pattern to use when you only want one instance of an object to be created.

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Singleton: Why use it?

• Don't waste resources
• Stay organized with name-spacing (aka module design pattern)

^may be used for handling database connection or http requests

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Singleton: Example Code #1

var MySingleton = {
  name: "Teddi",
  speak: function(){
    console.log("Hello");
  }
}

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Singleton: Example Code #2

var MySingleton = (function(){
  var privateValue = "secret";
  return {
    name: "Teddi",
    speak: function(){
      console.log("Hello");
    }
  }
})();

^ Does this look familiar? It looks like the module that we created yesterday which was also a Singleton.

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#[fit] The Facade Pattern

Build an Interface

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Facade: What is it?

• A facade is an object that provides a simplified interface to a larger body of code, such as a class library. -- Wikipedia

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Facade: Why use it?

• Only exposes what is necessary
• Can make the underlying functionality easier to consume
• Can be used to hide confusing or messy code
• Can be used to unify several sub-systems

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Facade: How to implement it:

• Create a function that will act as your facade.
• Access the original functions from inside of your facade.
• Create a new API that does what you need it to do.
• The end result is that you have a simpler interface.

^ Example - jQuery Example - legacy code with lots of different components, you create an interface on top of that. Whiteboard pic.

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Questions?