Element.shadowRoot

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.

Syntax

var shadowroot = element.shadowRoot;

Value

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).

Examples

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.

connectedCallback() {
  console.log('Custom square element added to page.');
  updateStyle(this);
}

attributeChangedCallback(name, oldValue, newValue) {
  console.log('Custom square element attributes changed.');
  updateStyle(this);
}

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')};
        }
      `;
    }
  });
}

Specifications

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

See also

© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/Element/shadowRoot