Add Missing JavaScript Implementations for Design Patterns

[mesalm]

Hi 👋,

While reviewing this great project, I noticed that some Design Patterns are implemented in TypeScript only, with no equivalent JavaScript implementations, like Singleton.

I’m wondering if this was intentional to maintain a specific structure, or if you're open to adding JavaScript versions for these patterns.

If there is interest in supporting JavaScript as well, I’d be glad to contribute, starting with Singleton and expanding to other patterns if it adds value.

If possible, it would be great to add a hacktoberfest label to help track these changes for Hacktoberfest.

Thanks in advance for considering, and I look forward to your thoughts on this proposal!