How do I use node as the middle tier?

  node.js, question

The purpose of using node as the middle layer is What? For example, java is used in the background. What problem does node solve if it is used as the middle layer? Are there any project examples?

1. Server rendering after separation of front and back ends
2. Communication between user information service terminals to verify and ensure safety
3. Distributed deployment of 3.node, high concurrency, etc