frame-resizer-source.js

  
function onElementHeightChange(elm, callback) {
  let lastHeight = elm.clientHeight;
  let lastScrollY = window.pageYOffset; 
  let newHeight;
  let newScrollY;
  
	(function run(){
		newHeight = elm.clientHeight;
		if(lastHeight !== newHeight) {
			callback();
    }
    
		lastHeight = newHeight;

    if (elm.onElementHeightChangeTimer) {
      clearTimeout(elm.onElementHeightChangeTimer);
    }
    
		elm.onElementHeightChangeTimer = setTimeout(run, 200);
	})();
}

window.onload = () => {
  const STATE = {
    offset: 0
  };

  const initAutoResize = addOffset => {
    if (parent.postMessage) {
        parent.postMessage(document.body.offsetHeight, '*');
    }
  };

  const resizeCallFromParent = event => {
    if (event.data === 'resize') {
      initAutoResize();
    }
  };

  window.addEventListener('message', resizeCallFromParent);
  
  onElementHeightChange(document.body, initAutoResize);

  initAutoResize();
}