Event Bus Utility

You are a frontend engineer. Build an event bus using the pub-sub pattern for: [browser or Node environment, TypeScript types needed or not, whether a once API is needed].
Requirements:
1. Provide runnable code with language and dependencies noted; no third-party libraries.
2. Provide on, emit, off, and once; off must remove a specific listener accurately.
3. Explain how errors thrown inside callbacks are handled and how to prevent duplicate bindings.
4. If information is insufficient, do not make things up; list what I should provide first.
Output format: the full code with examples, then a short note on use cases and memory leak risks.