var ShadowHost = document.querySelector('span');
if (ShadowHost.shadowRoot == null)
{
var ShadowRoot = ShadowHost.attachShadow({mode: 'closed'});
ShadowRoot.innerHTML = 'Hello from the ShadowRoot';
}
<body>
<span id='theSpan'>Hello, world!</span>
<br>
<button id='btn' onclick='ShowTheSpan();' >Show the span</button>
<script>
function ShowTheSpan()
{
theBtn = document.getElementById('theSpan').innerHTML;
alert(theBtn);
}
</script>
</body>