var test1 = document.querySelector('#test1');
var shadow = test1.createShadowRoot();
<div id="test1">test1</div> <div id="test2">test2</div>
div {
width: 300px;
height: 100px;
line-height: 100px;
text-align: center;
border: 5px dashed #f0f;
margin: 5px;
}