JS.16.02 Mid-levelCore — asked often

EventEmitter / pub-sub

Comes up in: Coding, Low-level design

This concept is being written. It gets the full five steps — explanation, predict, interview angle, practice with tests, and review cards. Here is exactly what it will cover, so you can study it elsewhere in the meantime.

What it covers

on, off, once, emit
unsubscribe function
removing during emit (copy listeners)
error event
wildcard (bonus)

Words you will know

observer patternpublish-subscribe

What you will practise

implement (worked → timed)

Interview questions this answers

Implement an EventEmitter with on, off, once and emit.