Lære Singleton Pattern | Creational Patterns

JavaScript Design Patterns

The Singleton pattern is a creational design pattern that restricts the instantiation of a class to one single object. In JavaScript, this pattern is especially useful when you need to coordinate actions across the system using a single shared resource. Common use cases include managing a single database connection; handling configuration settings; or maintaining a single logging instance. By ensuring that only one instance exists, you avoid issues such as conflicting states or unnecessary resource consumption.


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// Simple Singleton implementation using an object
const Singleton = (function() {
  let instance;

  function createInstance() {
    return {
      message: "I am the only instance!"
    };
  }

  return {
    getInstance: function() {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();

// Usage
const singletonA = Singleton.getInstance();
const singletonB = Singleton.getInstance();

console.log(singletonA === singletonB); // true
console.log(singletonA.message); // "I am the only instance!"

This Singleton implementation works by using a closure to keep the instance variable private. When you call getInstance(), it checks if an instance already exists. If not, it creates one and stores it. Any subsequent calls to getInstance() will return the same object. This ensures that throughout your code, there is only one instance of the Singleton, and any changes to it are shared everywhere it is accessed.

1. What is the main purpose of the Singleton pattern?

2. In JavaScript, a Singleton is often implemented using:

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              1234567891011121314151617181920212223242526
            
// Simple Singleton implementation using an object
const Singleton = (function() {
  let instance;

  function createInstance() {
    return {
      message: "I am the only instance!"
    };
  }

  return {
    getInstance: function() {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();

// Usage
const singletonA = Singleton.getInstance();
const singletonB = Singleton.getInstance();

console.log(singletonA === singletonB); // true
console.log(singletonA.message); // "I am the only instance!"

1. What is the main purpose of the Singleton pattern?

2. In JavaScript, a Singleton is often implemented using:

Var alt klart?

Tak for dine kommentarer!

Sektion 2. Kapitel 1