Fix the broken EventEmitter

A bug report arrived from the analytics team: dashboard components keep receiving real-time updates even after calling off() to unsubscribe from a feed. The EventEmitter that drives the live data pipeline is the suspect.

The code compiles. TypeScript is happy. But two of the three tests are red — and the failure only shows up when you try to unsubscribe.

The situation

const handler = (v: number) => display(v)

emitter.on<number>("price-update", handler)
emitter.emit("price-update", 42) // ✓ handler called

emitter.off<number>("price-update", handler)
emitter.emit("price-update", 99) // ✗ handler still called — why?

What you'll practice

• How JavaScript compares function references with ===
• Why wrapping a function creates a new identity, even if the behavior is the same
• The pattern used by every major event system (DOM, Node.js, RxJS) to make off() work

Done when

• All three tests pass
• off() correctly removes only the specified listener
• Other listeners registered on the same event remain active