next.js/test/unit/mitt.test.ts

/* eslint-env jest */
import mitt from 'next/dist/shared/lib/mitt'

describe('mitt', () => {
  describe('With listeners', () => {
    it('should listen to an event', () => {
      return new Promise((resolve) => {
        const ev = mitt()
        ev.on('sample', resolve)
        ev.emit('sample')
      })
    })

    it('should listen to multiple listeners', () => {
      const ev = mitt()
      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 = mitt()
      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 = mitt()
      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 = mitt()
      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)
    })
  })

  describe('Without a listener', () => {
    it('should not fail to emit', () => {
      const ev = mitt()
      ev.emit('aaaa', 10, 20)
    })
  })
})