does stuff when things are added to the page... via https://github.com/muicss/sentineljs

injectSientinal.js

(function(style, func){
document.addEventListener('sentinel-load', function(){
   sentinel.on(style, func);
})
var a=document.createElement("script");a.src='//cdn.rawgit.com/muicss/sentineljs/0.0.4/dist/sentinel.min.js';a.type="text/javascript";
document.head.appendChild(a);
})('.my-div', function(el) {
  el.innerHTML = 'The sentinel is always watching.';
})