Event Emitter From Scratch | Dataford Interview Questions

Implement an event emitter from scratch.

Implement event_emitter(operations) using only data structures. Support registering persistent listeners with on, registering one-time listeners with once, removing listeners with off, and dispatching events with emit.

Each operation is an array. Listener identifiers are strings, and each emit operation returns the listener identifiers invoked in registration order. Return the outputs from all emit operations.

Constraints

1 <= len(operations) <= 1000
Each operation is one of: ["on", event, listener_id], ["once", event, listener_id], ["off", event, listener_id], or ["emit", event, payload]
event and listener_id are non-empty strings
payload is optional JSON-compatible data and does not affect listener selection
Listeners are invoked in registration order
An off operation removes all registrations matching the event and listener identifier

Function Signature

def event_emitter(operations):

Whenever you're ready, walk me through your approach or go straight to the code. The requirements are in the Question tab.

Problem

Implement an event emitter from scratch.

Each operation is an array. Listener identifiers are strings, and each emit operation returns the listener identifiers invoked in registration order. Return the outputs from all emit operations.

Constraints

1 <= len(operations) <= 1000
Each operation is one of: ["on", event, listener_id], ["once", event, listener_id], ["off", event, listener_id], or ["emit", event, payload]
event and listener_id are non-empty strings
payload is optional JSON-compatible data and does not affect listener selection
Listeners are invoked in registration order
An off operation removes all registrations matching the event and listener identifier

Function Signature

def event_emitter(operations):

Whenever you're ready, walk me through your approach or go straight to the code. The requirements are in the Question tab.