Singleton

Now, we are going to spend a few words on a pattern that is among the most used in object-oriented programming, which is the Singleton pattern. As we will see, Singleton is one of those patterns that has a trivial implementation in Node.js that's almost not worth discussing. However, there are a few caveats and limitations that every good Node.js developer must know.

The purpose of the Singleton pattern is to enforce the presence of only one instance of a class and centralize its access. There are a few reasons for using a single instance across all the components of an application:

• For sharing stateful information
• For optimizing resource usage
• To synchronize access to a resource

As you can imagine, those are quite common scenarios. Take, for example, a typical Database class, which provides access to a database:

// 'Database.js'
export class Database {
  constructor (dbName, connectionDetails) {
    // ...
  }
  //...