function makeIframe (src) {
    if (!src) throw new Error('meh')
    const iframe = document.createElement('iframe')
    iframe.hidden = true
    iframe.src = src
    iframe.loaded = false
    iframe.name = 'iframe'
    iframe.isIframe = true
    iframe.postMessage = (...args) => iframe.contentWindow.postMessage(...args)
    iframe.addEventListener('load', () => {
      iframe.loaded = true
    }, { once: true })
    document.body.appendChild(iframe)
    return iframe
  }
create a hidden iframe and append it to the DOM (body)

@param  {string} src page to load
@return {HTMLIFrameElement} page to load