The read-only composed
property of the Event
interface returns a Boolean
which indicates whether or not the event will propagate across the shadow DOM boundary into the standard DOM.
Note: This property was formerly named scoped
.
Syntax
const isComposed = Event.composed;
Value
A Boolean
which is true
if the event will cross from the shadow DOM into the standard DOM after reaching the shadow root. (That is, the first node in the shadow DOM in which the event began to propagate.)
All UA-dispatched UI events are composed (click/touch/mouseover/copy/paste, etc.). Most other types of events are not composed, and so will return false
. For example, this includes synthetic events that are created without their composed
option wil set to true
.
Propagation only occurs if the bubbles
property is also true
. However, capturing only composed events are also handled at host as if they were in AT_TARGET
phase. You can determine the path the event will follow through the shadow root to the DOM root by calling composedPath()
.
If this value is false
, the shadow root will be the last node to be offered the event.
Examples
In our composed-composed-path example (see it live), we define two trivial custom elements, <open-shadow>
and <closed-shadow>
, both of which take the contents of their text attribute and insert them into the element's shadow DOM as the text content of a <p>
element. The only difference between the two is that their shadow roots are attached with their modes set to open
and closed
respectively.
The first definition looks like this, for example:
customElements.define('open-shadow',
class extends HTMLElement {
constructor() {
super();
let pElem = document.createElement('p');
pElem.textContent = this.getAttribute('text');
let shadowRoot = this.attachShadow({mode: 'open'})
.appendChild(pElem);
}
});
We then insert one of each element into our page:
<open-shadow text="I have an open shadow root"></open-shadow>
<closed-shadow text="I have a closed shadow root"></closed-shadow>
Then include a click event listener on the <html>
element:
document.querySelector('html').addEventListener('click',function(e) {
console.log(e.composed);
console.log(e.composedPath());
});
When you click on the <open-shadow>
element and then the <closed-shadow>
element, you'll notice two things.
- The
composed
property returnstrue
beause theclick
event is always able to propagate across shadow boundaries. - You'll notice a difference in the value of
composedPath
for the two elements.
The <open-shadow>
element's composed path is this:
Array [ p, ShadowRoot, open-shadow, body, html, HTMLDocument https://mdn.github.io/web-components-examples/composed-composed-path/, Window ]
Whereas the <closed-shadow>
element's composed path is a follows:
Array [ closed-shadow, body, html, HTMLDocument https://mdn.github.io/web-components-examples/composed-composed-path/, Window ]
In the second case, the event listeners only propagate as far as the <closed-shadow>
element itself, but not to the nodes inside the shadow boundary.
Specifications
Specification | Status | Comment |
---|---|---|
DOMThe definition of 'composed' in that specification. | Living Standard |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
composed
|
Chrome
Full support 53 |
Edge
Full support 79 |
Firefox
Full support 52 |
IE
No support No |
Opera
Full support 40 |
Safari
Full support Yes |
WebView Android
Full support 53 |
Chrome Android
Full support 53 |
Firefox Android
Full support 52 |
Opera Android
Full support 41 |
Safari iOS
Full support Yes |
Samsung Internet Android
Full support 6.0 |
Legend
- Full support
- Full support
- No support
- No support
Event.composed by Mozilla Contributors is licensed under CC-BY-SA 2.5.