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class EventEmitter<T extends object> { | |
listeners: { [K in keyof T]?: Set<(data: T[K]) => void> } = {}; | |
on<K extends keyof T>(name: K, cb: (data: T[K]) => void) { | |
const listeners = this.listeners[name] ?? new Set(); | |
listeners.add(cb); | |
this.listeners[name] = listeners; | |
return () => listeners.delete(cb); | |
} | |
emit<K extends keyof T>(name: K, data: T[K]) { | |
const listeners = this.listeners[name] ?? new Set(); | |
listeners.forEach((fn) => fn(data)); | |
} | |
} | |
const eventEmitter = const EventEmitter<{ data: number, error: Error }>() | |
eventEmitter.on('data', data => ...) // data: number | |
eventEmitter.on('error', err => ...) // err: Error | |
eventEmitter.emit('data', "oops") // ❌ expected number | |
eventEmitter.emit('error', new Error("✅")) | |
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