post.js

;(function () {
  const on = window.addEventListener
  let parent = null

  const _post = function () {
    parent.postMessage(
      {
        type: 'FRAME_HEIGHT',
        height: document.documentElement.scrollHeight,
      },
      '*'
    )
  }

  const post = function () {
    let timer = null
    clearTimeout(timer)
    if (parent) {
      timer = setTimeout(_post, 250)
    }
  }

  on('message', function (event) {
    parent = event.source
    post()
  })

  on('resize', post)
  on('load', post)

  new MutationObserver(function () {
    post()
  }).observe(document.querySelector('body'), {
    childList: true,
    attributes: true,
    characterData: true,
    subtree: true,
    attributeOldValue: true,
    characterDataOldValue: true,
  })
})()