Reflow Demo

HTML

<body>
  <button id="btn">Btn</button>
  <button id="btndf">Btn Document fragment</button>
  <button id="clear">Clear</button>
<div id="wrapper">

</div>

CSS

#wrapper div {
  background: red;
  display: block;
  width: 100px;
  height: 100px;
}

JavaScript

var wrapper = document.getElementById("wrapper");
  document.getElementById("btn").addEventListener('click',function(){
    var n=100;
    while(n--){
      var inner = document.createElement('div');
      inner.innerHTML = "Inner" + n;
      wrapper.appendChild(inner);
      inner.outerWidth =inner.outerWidth + 1 ;
    }
  });

  document.getElementById("btndf").addEventListener('click',function(){
    var df = document.createDocumentFragment();
    var n=100;
    while(n--){
      var inner = document.createElement('div');
      inner.innerHTML = "Inner" + n;
      df.appendChild(inner);
    }
    wrapper.appendChild(df);
  })

  document.getElementById("clear").addEventListener('click', function(){
    wrapper.innerHTML = "";
  });