on(eventName, listener)

Registers a listener for a given event. Multiple listeners can be registered for the same event.

Parameters:

• eventName (string) – Name of the event to listen to.
• listener (function) – Callback function to execute when the event is emitted.

Returns: The EventEmitter instance (supports chaining).

Example:

          
            1const emitter = new EventEmitter();3emitter.on("data", (msg) => {4  console.log("Received:", msg);5});7emitter.emit("data", "Hello World"); // Logs: Received: Hello World
          
        

Edge Cases:

• Multiple listeners can be attached to the same event; all will be called in order of registration.
• Chaining allows multiple on calls in sequence: emitter.on("a", fn1).on("b", fn2).

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