/Web APIs

Element: shadowRoot property

The Element.shadowRoot read-only property represents the shadow root hosted by the element.

Use Element.attachShadow() to add a shadow root to an existing element.


A ShadowRoot object instance, or null if the associated shadow root was attached with its mode set to closed. (See Element.attachShadow() for further details).


The following snippets are taken from our life-cycle-callbacks example (see it live also), which creates an element that displays a square of a size and color specified in the element's attributes.

Inside the <custom-square> element's class definition we include some life cycle callbacks that make a call to an external function, updateStyle(), which actually applies the size and color to the element. You'll see that we are passing it this (the custom element itself) as a parameter.

class Square extends HTMLElement {
  connectedCallback() {
    console.log("Custom square element added to page.");

  attributeChangedCallback(name, oldValue, newValue) {
    console.log("Custom square element attributes changed.");

In the updateStyle() function itself, we get a reference to the shadow DOM using Element.shadowRoot. From here we use standard DOM traversal techniques to find the <style> element inside the shadow DOM and then update the CSS found inside it:

function updateStyle(elem) {
  const shadow = elem.shadowRoot;
  const childNodes = Array.from(shadow.childNodes);

  childNodes.forEach((childNode) => {
    if (childNode.nodeName === "STYLE") {
      childNode.textContent = `
        div {
          width: ${elem.getAttribute("l")}px;
          height: ${elem.getAttribute("l")}px;
          background-color: ${elem.getAttribute("c")};


Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
shadowRoot 35 79 63 No 22 10 37 35 63 22 10 3.0

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