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Starter#Design Patterns#Polyfill
EventEmitter Polyfill
Implement a pub/sub EventEmitter class with on, off, emit, and once — the pattern behind Node's events module.
By modernDev2026-06-05Medium
An EventEmitter is the publish/subscribe pattern: register listeners with on, remove them with off, fire them with emit, and register one-time listeners with once. Two details interviewers watch for: iterating over a copy of the listener array in emit (so a self-removing listener doesn't corrupt the loop), and the once wrapper that unregisters itself by reference.
Goal: Implement all four EventEmitter methods. Pay attention to the .slice() in emit and the wrapper in once.
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