Full width iframes (for example, videos)

iframes.js

(function () {
  let ratios = [];

  let resizeIframes = function (iframes, ratio) {
  	let winW = window.innerWidth;
  	iframes.forEach( (iframe,i) => {
  		let [w, h] = [iframe.clientWidth, iframe.clientHeight],
  				_ratio = ratio && ratio[i] || h/w;
  		// set iframe size
  		iframe.style.height = winW*_ratio+'px';
  		iframe.style.width = '100%';
  		// if first call, store original iframe ratio
  		if (ratios.length !== iframes.length) { ratios.push(_ratio);}
  	});
  };
  // poll until iframes are inserted in the dom
  let pollIframe = function () {
  	let iframes = document.querySelectorAll('iframe');
  	if (iframes.length === 0) {
  		return setTimeout(pollIframe, 100);
  	}
  	let iframesList = [].slice.call(iframes);
  	resizeIframes(iframesList);
  	// listen to resize event
  	window.addEventListener('resize', function () {
  		resizeIframes(iframesList, ratios);
  	});
  };
})();