Moving iframe from one element to another

window.onresize = readjustTheForm;
var current = 'desktop';

function readjustTheForm()
{
  //mobile - #xr_xd65
  //desktop - #xr_xrc9 > .xr_noreset

  if(window.width < 720 && current === 'desktop')
  {
     document.getElementById('xr_xd65').appendChild( document.getElementById('JotFormIframe') );
     current = 'mobile';
  }
  else if(window.width > 719 && current === 'mobile')
  {
    document.getElementById('xr_xrc9').getElementsByClassName('xr_noreset').appendChild( document.getElementById('JotFormIframe') );
    current = 'desktop';
  }
}