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next.js/packages/next-server/lib/EventEmitter.js

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export default class EventEmitter {
listeners = {}
on (event, cb) {
if (!this.listeners[event]) {
this.listeners[event] = new Set()
}
2017-07-09 03:46:53 +00:00
if (this.listeners[event].has(cb)) {
throw new Error(`The listener already exising in event: ${event}`)
}
this.listeners[event].add(cb)
return this
}
emit (event, ...data) {
const listeners = this.listeners[event]
const hasListeners = listeners && listeners.size
if (!hasListeners) {
return false
}
listeners.forEach(cb => cb(...data)) // eslint-disable-line standard/no-callback-literal
return true
}
off (event, cb) {
this.listeners[event].delete(cb)
return this
}
}