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 resize-observer-text.html (see source) example, we use the resize observer to change the font-size
of a header and paragraph as a sliderโs value is changed causing the containing <div>
to change width. This shows that you can respond to changes in an elementโs 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 (const entry of entries) { if (entry.contentBoxSize) { 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'; } } }); resizeObserver.observe(divElem); checkbox.addEventListener('change', () => { if (checkbox.checked) { resizeObserver.observe(divElem); } else { resizeObserver.unobserve(divElem); } });
Specifications
Specification | Status | Comment |
---|---|---|
Resize Observer The definition of 'ResizeObserver' in that specification. |
Editor's Draft | Initial definition. |
Browser compatibility
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