code: function watchForRender(node, handler) {
  	var expando = node[EXPANDO_KEY] || (node[EXPANDO_KEY] = {});
  	var proxy = expando.renderProxy = function(e) {
  		if (e.animationName === CSS_RENDER_ANIMATION) {
  			handler();
  		}
  	};
  
  	helpers$1.each(ANIMATION_START_EVENTS, function(type) {
  		addListener(node, type, proxy);
  	});
  
  	// #4737: Chrome might skip the CSS animation when the CSS_RENDER_MONITOR class
  	// is removed then added back immediately (same animation frame?). Accessing the
  	// `offsetParent` property will force a reflow and re-evaluate the CSS animation.
  	// https://gist.github.com/paulirish/5d52fb081b3570c81e3a#box-metrics
  	// https://github.com/chartjs/Chart.js/issues/4737
  	expando.reflow = !!node.offsetParent;
  
  	node.classList.add(CSS_RENDER_MONITOR);
  }
docs: https://davidwalsh.name/detect-node-insertion