Waiting for define deep property in window object

42.js

const waitForProp = (prop, context) => new Promise(resolve => {
  if (typeof context[prop] !== 'undefined') {
    resolve(context[prop])
    return
  }

  const desc = Object.getOwnPropertyDescriptor(context, prop)
  if (desc) {
    Object.defineProperty(context, prop, {
      set(value) {
        resolve(value)
        desc.set(value)
      }
    })
  } else {
    let targetProperty
    Object.defineProperty(context, prop, {
      get() {
        return targetProperty
      },
      set(value) {
        targetProperty = value
        resolve(value)
      },
      configurable: true
    })
  }
})

const waitForPath = path => path
  .split('.')
  .reduce(
    (acc, cur) => acc
      .then(ctx => waitForProp(cur, ctx)),
    Promise.resolve(window)
  )

waitForPath('zzz.xxx.mmm').then(() => { console.log('aaa') })
waitForPath('zzz.xxx').then(() => { console.log('bbb') })
waitForPath('zzz').then(() => { console.log('ccc') })

setTimeout(() => { window.zzz = { xxx: { mmm: true }} }, 1000)