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next.js/test/unit/EventEmitter.test.js
Jacob Page b492e6703d Make EventEmitter more Node-like (#4865)
Add behaviors to make `EventEmitter` a bit more like its NodeJS counterpart. This should make using it a bit less surprising.
2018-08-01 14:43:25 +02:00

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JavaScript

/* global describe, it, expect */
import EventEmitter from '../../dist/lib/EventEmitter'
describe('EventEmitter', () => {
describe('With listeners', () => {
it('should listen to a event', (done) => {
const ev = new EventEmitter()
ev.on('sample', done)
ev.emit('sample')
})
it('should listen to multiple listeners', () => {
const ev = new EventEmitter()
let cnt = 0
ev.on('sample', () => { cnt += 1 })
ev.on('sample', () => { cnt += 1 })
ev.emit('sample')
expect(cnt).toBe(2)
})
it('should listen to multiple events', () => {
const ev = new EventEmitter()
const data = []
const cb = (name) => { data.push(name) }
ev.on('sample1', cb)
ev.on('sample2', cb)
ev.emit('sample1', 'one')
ev.emit('sample2', 'two')
expect(data).toEqual(['one', 'two'])
})
it('should support multiple arguments', () => {
const ev = new EventEmitter()
let data
ev.on('sample', (...args) => { data = args })
ev.emit('sample', 'one', 'two')
expect(data).toEqual(['one', 'two'])
})
it('should possible to stop listening an event', () => {
const ev = new EventEmitter()
let cnt = 0
const cb = () => { cnt += 1 }
ev.on('sample', cb)
ev.emit('sample')
expect(cnt).toBe(1)
ev.off('sample', cb)
ev.emit('sample')
expect(cnt).toBe(1)
})
it('should throw when try to add the same listener multiple times', () => {
const ev = new EventEmitter()
const cb = () => {}
ev.on('sample', cb)
const run = () => ev.on('sample', cb)
expect(run).toThrow(/The listener already exising in event: sample/)
})
it('should support chaining like the nodejs EventEmitter', () => {
const emitter = new EventEmitter()
let calledA = false
let calledB = false
emitter
.on('a', () => { calledA = true })
.on('b', () => { calledB = true })
emitter.emit('a')
emitter.emit('b')
expect(calledA).toEqual(true)
expect(calledB).toEqual(true)
})
it('should return an indication on emit if there were listeners', () => {
const emitter = new EventEmitter()
emitter.on('a', () => { })
expect(emitter.emit('a')).toEqual(true)
expect(emitter.emit('b')).toEqual(false)
})
})
describe('Without a listener', () => {
it('should not fail to emit', () => {
const ev = new EventEmitter()
ev.emit('aaaa', 10, 20)
})
})
})