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.


var shadowroot = element.shadowRoot; 


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.

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) {
  var shadow = elem.shadowRoot;
  var childNodes = shadow.childNodes;
  for(var i = 0; i < childNodes.length; i++) {
    if(childNodes[i].nodeName === 'STYLE') {
      childNodes[i].textContent = 'div {' +
                          ' width: ' + elem.getAttribute('l') + 'px;' +
                          ' height: ' + elem.getAttribute('l') + 'px;' +
                          ' background-color: ' + elem.getAttribute('c');


Specification Status Comment
The definition of 'shadowRoot' in that specification.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support53 No1592 3 No40 Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support5353 No1592 340 Yes ?

1. Under consideration

2. See bug 1205323

3. From version 59: this feature is behind the dom.webcomponents.shadowdom.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.

Document Tags and Contributors

Last updated by: ExE-Boss,