I don't know, Angular.js used to create factories in this way

Singletons are used to share information between different areas of your application. They can not be considered anti-pattern as the provide a functionality that won't exisits without them. As a developer, you need to understand when is appropriate to define services in a singleton way. If you don't understand their functionality then, of course, they can lead to problems. However that is nothing to do with the singletons themselves but with the developer who use them in an inappropriate way.

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