Trying to create an onboarding document for junior devs. What are the must-have items?

Here are my 2 cents:

• First of all I think the onboarding period is often too short. I observed that 3-4 weeks of preparations are of most help to new employees (with no or little professional experience)
• Onboarding activities should be well documented.

Here are several real-world examples I created for a node.js backend developer that takes ± a month:

• Development methodology
• Programming Paradigms (Event loop, Promise chaining (for legacy codes), async-await, functional programming, ES6, exception handling)
• Most frequently used libraries (mocha, sequelize, express, async etc.)
• Version Control System (Git)
• Tools (VS Code, ESLint, debugging)
• In house libraries
• Actual Code Structure
• A task in the sprint (TBD later on)