As there are many way for implementation, it would be chaos if no standard for implementation.
How would you guide the junior devloper to follow the same way?
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My take on your question
Any documentation is better than no documentation. Get in the habit of writing development notes a la Wiki and make it accessible to the whole team. My biggest issue when joining as a junior dev was that I had to ask even the simplest questions about the codebase because there were no notes or documents on the application at all.
I've found its very helpful to have a set of tools and documentation you can have them try to conform to right away, with the guidance of a dedicated mentor.