Singleton Pattern

Now, we’re going to spend a few words on a pattern that’s among the most used in object-oriented programming, which is the Singleton pattern. As we’ll 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 should 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

These are some really common scenarios.

Example

Take, for example, a typical Database class, which provides access to a database.