Learning JavaScript Design Patterns

The Singleton Pattern

The Singleton pattern is thus known because it restricts instantiation of a class to a single object. Classically, the Singleton pattern can be implemented by creating a class with a method that creates a new instance of the class if one doesn’t exist. In the event of an instance already existing, it simply returns a reference to that object. Singletons differ from static classes (or objects) as we can delay their initialization, generally because they require some information that may not be available during initialization time. For code that is unaware of a previous reference to them, they do not provide a method for easy retrieval. This is because it is neither the object nor “class” that’s returned by a Singleton; it’s a structure. Think of how closured variables aren’t actually closures—the function scope that provides the closure is the closure. In JavaScript, Singletons serve as a shared resource namespace which isolate implementation code from the global namespace so as to provide a single point of access for functions. We can implement a Singleton as follows:

var mySingleton = (function () { // Instance stores a reference to the Singleton var instance; function init() { // Singleton // Private methods and variables function privateMethod(){ console.log( "I am private" ); } var privateVariable = "Im also private"; var privateRandomNumber = Math.random(); return { // Public methods and variables publicMethod: function () { console.log( "The public can ...