ople-forwardListeners.js

import {expectOple} from 'ople'

// Note: Unique function values are expected.
export function forwardListeners(listenFns) {
  const disposeFns = new Map()
  const self = expectOple()
  hookBefore(self, {
    _addListener(key, fn) {
      if (!listenFns[key]) return
      disposeFns.set(fn, listenFns[key](fn))
    },
    _removeListener(key, fn) {
      if (!listenFns[key]) return
      disposeFns.get(key)()
    },
  })
}

function hookBefore(self, hooks) {
  for (const name in fns) {
    const orig = self[name]
    self[name] = (...args) => {
      hooks[name].apply(self, args)
      orig.apply(self, args)
    }
  }
}

export const listen = (source, type) => (fn) => {
  source.on(type, fn)
  return () => source.off(type, fn)
}

//
// DEMO
//

const api = new Ople()
const demo = new Ople(self => {
  forwardListeners({
    test: listen(api, 'test'),
  })
})

demo.on('test', console.log)

// Emits from either are logged.
api.emit('test', 'hello')
demo.emit('test', 'world')