The ResizeObserver
interface reports changes to the dimensions of an Element
's content or border box, or the bounding box of an SVGElement
.
Note: The content box is the box in which content can be placed, meaning the border box minus the padding and border width. The border box encompasses the content, padding, and border. See The box model for further explanation.
ResizeObserver
avoids infinite callback loops and cyclic dependencies that are often created when resizing via a callback function. It does this by only processing elements deeper in the DOM in subsequent frames. Implementations should, if they follow the specification, invoke resize events before paint and after layout.
Constructor
ResizeObserver()
- Creates and returns a new
ResizeObserver
object.
Properties
None.
Methods
ResizeObserver.disconnect()
- Unobserves all observed
Element
targets of a particular observer. ResizeObserver.observe()
- Initiates the observing of a specified
Element
. ResizeObserver.unobserve()
- Ends the observing of a specified
Element
.
Examples
In the [[../../../../../../mdn.github.io/dom-examples/resize-observer/resize-observer-text|resize-observer-text.html]] (see source) example, we use the resize observer to change the font-size
of a header and paragraph as a slider’s value is changed causing the containing <div>
to change width. This shows that you can respond to changes in an element’s size, even if they have nothing to do with the viewport.
We also provide a checkbox to turn the observer off and on. If it is turned off, the text will not change in response to the <div>
's width changing.
The JavaScript looks like so:
const h1Elem = document.querySelector('h1');
const pElem = document.querySelector('p');
const divElem = document.querySelector('body > div');
const slider = document.querySelector('input[type="range"]');
const checkbox = document.querySelector('input[type="checkbox"]');
divElem.style.width = '600px';
slider.addEventListener('input', () => {
divElem.style.width = slider.value + 'px';
})
const resizeObserver = new ResizeObserver(entries => {
for (let entry of entries) {
if(entry.contentBoxSize) {
// Checking for chrome as using a non-standard array
if (entry.contentBoxSize[0]) {
h1Elem.style.fontSize = Math.max(1.5, entry.contentBoxSize[0].inlineSize/200) + 'rem';
pElem.style.fontSize = Math.max(1, entry.contentBoxSize[0].inlineSize/600) + 'rem';
} else {
h1Elem.style.fontSize = Math.max(1.5, entry.contentBoxSize.inlineSize/200) + 'rem';
pElem.style.fontSize = Math.max(1, entry.contentBoxSize.inlineSize/600) + 'rem';
}
} else {
h1Elem.style.fontSize = Math.max(1.5, entry.contentRect.width/200) + 'rem';
pElem.style.fontSize = Math.max(1, entry.contentRect.width/600) + 'rem';
}
}
console.log('Size changed');
});
resizeObserver.observe(divElem);
checkbox.addEventListener('change', () => {
if (checkbox.checked) {
resizeObserver.observe(divElem);
} else {
resizeObserver.unobserve(divElem);
}
});
Specifications
Specification | Status | Comment |
Resize ObserverThe definition of 'ResizeObserver' in that specification. | Editor's Draft | Initial definition. |
Browser compatibility
The compatibility table in 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 | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
ResizeObserver
|
Chrome
Full support 64 |
Edge
Full support 79 |
Firefox
Full support 69 |
IE
No support No |
Opera
Full support 51 |
Safari
Full support 13.1 |
WebView Android
Full support 64 |
Chrome Android
Full support 64 |
Firefox Android
No support No |
Opera Android
Full support 47 |
Safari iOS
Full support 13.4 |
Samsung Internet Android
Full support 9.0 |
ResizeObserver() constructor
|
Chrome
Full support 64 |
Edge
Full support 79 |
Firefox
Full support 69 |
IE
No support No |
Opera
Full support 51 |
Safari
Full support 13.1 |
WebView Android
Full support 64 |
Chrome Android
Full support 64 |
Firefox Android
No support No |
Opera Android
Full support 47 |
Safari iOS
Full support 13.4 |
Samsung Internet Android
Full support 9.0 |
disconnect
|
Chrome
Full support 64 |
Edge
Full support 79 |
Firefox
Full support 69 |
IE
No support No |
Opera
Full support 51 |
Safari
Full support 13.1 |
WebView Android
Full support 64 |
Chrome Android
Full support 64 |
Firefox Android
No support No |
Opera Android
Full support 47 |
Safari iOS
Full support 13.4 |
Samsung Internet Android
Full support 9.0 |
observe
|
Chrome
Full support 64 |
Edge
Full support 79 |
Firefox
Full support 69 |
IE
No support No |
Opera
Full support 51 |
Safari
Full support 13.1 |
WebView Android
Full support 64 |
Chrome Android
Full support 64 |
Firefox Android
No support No |
Opera Android
Full support 47 |
Safari iOS
Full support 13.4 |
Samsung Internet Android
Full support 9.0 |
unobserve
|
Chrome
Full support 64 |
Edge
Full support 79 |
Firefox
Full support 69 |
IE
No support No |
Opera
Full support 51 |
Safari
Full support 13.1 |
WebView Android
Full support 64 |
Chrome Android
Full support 64 |
Firefox Android
No support No |
Opera Android
Full support 47 |
Safari iOS
Full support 13.4 |
Samsung Internet Android
Full support 9.0 |
Legend
- Full support
- Full support
- No support
- No support
See also
ResizeObserver by Mozilla Contributors is licensed under CC-BY-SA 2.5.