这是一个例子：

var container = document.querySelector('#example');
//Create shadow root !
var root = container.createShadowRoot();
root.innerHTML = '<div>Root<div class="test">Element in shadow</div></div>';

//Access the element inside the shadow !
//"container.shadowRoot" represents the youngest shadow root that is hosted on the element !
console.log(container.shadowRoot.querySelector(".test").innerHTML);

演示：

var container = document.querySelector('#example');

//Create shadow root !

var root = container.createShadowRoot();

root.innerHTML = '<div>Root<div class="test">Element in shadow</div></div>';



//Access the element inside the shadow !

console.log(container.shadowRoot.querySelector(".test").innerHTML);


<div id="example">Element</div>

我希望这能帮到您。