var callback=function(){

  console.log("Dom changed");

};

var mutationObserver=new MutationObserver(callback);

var otpions={

  subtree:true,

  childList:true

};

mutationObserver.observe(document.body,otpions);

var arr=mutationObserver.takeRecords();

console.log(arr);

window.onload=function(){

  for(var i=0;i<10;i++){

    var li=document.createElement("li");

    li.innerText="这是";

 document.getElementById("container").appendChild(li);

  }

};