The Element.attachShadow()
method attaches a shadow DOM tree to the specified element and returns a reference to its ShadowRoot
.
Element.attachShadow()
Elements you can attach a shadow to
Note that you can't attach a shadow root to every type of element. There are some that can't have a shadow DOM for security reasons (for example <a>
).
The following is a list of elements you can attach a shadow root to:
Syntax
attachShadow(init)
Parameters
-
init
-
A object that contain the following fields:
-
mode
-
A string specifying the encapsulation mode for the shadow DOM tree. This can be one of:
-
open
: Elements of the shadow root are accessible from JavaScript outside the root, for example usingElement.shadowRoot
:element.shadowRoot; // Returns a ShadowRoot obj
-
closed
: Denies access to the node(s) of a closed shadow root from JavaScript outside it:element.shadowRoot; // Returns null
-
-
delegatesFocus
-
A boolean that, when set to
true
, specifies behavior that mitigates custom element issues around focusability. When a non-focusable part of the shadow DOM is clicked, the first focusable part is given focus, and the shadow host is given any available:focus
styling.
-
Return value
Returns a ShadowRoot
object.
Exceptions
-
InvalidStateError
-
The element you are trying to attach to is already a shadow host.
-
NotSupportedError
-
You are trying to attach a shadow root to an element outside the HTML namespace, the element cannot have a shadow attached to it, or the static property
disabledFeatures
has been given a value of"shadow"
in the element definition.
Examples
The following example is taken from our word-count-web-component demo (see it live also). You can see that we use attachShadow()
in the middle of the code to create a shadow root, which we then attach our custom element's contents to.
// Create a class for the element class WordCount extends HTMLParagraphElement { constructor() { // Always call super first in constructor super(); // count words in element's parent element const wcParent = this.parentNode; function countWords(node){ const text = node.innerText || node.textContent; return text.trim().split(/\s+/g).filter(a => a.trim().length > 0).length; } const count = `Words: ${countWords(wcParent)}`; // Create a shadow root const shadow = this.attachShadow({mode: 'open'}); // Create text node and add word count to it const text = document.createElement('span'); text.textContent = count; // Append it to the shadow root shadow.appendChild(text); // Update count when element content changes setInterval(function() { const count = `Words: ${countWords(wcParent)}`; text.textContent = count; }, 200); } } // Define the new element customElements.define('word-count', WordCount, { extends: 'p' });
Specifications
Specification |
---|
DOM Standard # ref-for-dom-element-attachshadow① |
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 | |
attachShadow |
53
|
79
|
63
|
No
|
40
|
10
|
53
|
53
|
63
|
41
|
10
|
6.0
|
init_delegatesFocus_parameter |
53
|
79
|
94
|
No
|
40
|
13.1
|
53
|
53
|
94
|
41
|
13.4
|
6.0
|
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/attachShadow