This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The contentBoxSize
read-only property of the ResizeObserverEntry
interface returns an array containing the new content box size of the observed element when the callback is run.
Syntax
var myContentBoxSize = ResizeObserverEntry.contentBoxSize;
Value
An object containing the new content box size of the observed element. This object contains two properties:
blockSize
- The length of the observed element's content box in the block dimension. For boxes with a horizontal
writing-mode
, this is the vertical dimension, or height; if the writing-mode is vertical, this is the horizontal dimension, or width. inlineSize
- The length of the observed element's content box in the inline dimension. For boxes with a horizontal
writing-mode
, this is the horizontal dimension, or width; if the writing-mode is vertical, this is the vertical dimension, or height.
Note: For more explanation of writing modes and block and inline dimensions, read Handling different text directions.
Examples
The following snippet is taken from the resize-observer-border-radius.html (see source) example. This example includes a green box, sized as a percentage of the viewport size. When the viewport size is changed, the box's rounded corners change in proportion to the size of the box. We could just implement this using border-radius
with a percentage, but that quickly leads to ugly-looking elliptical corners; this solution gives you nice square corners that scale with the box size.
const resizeObserver = new ResizeObserver(entries => { for (let entry of entries) { if(entry.contentBoxSize) { entry.target.style.borderRadius = Math.min(100, (entry.contentBoxSize.inlineSize/10) + (entry.contentBoxSize.blockSize/10)) + 'px'; } else { entry.target.style.borderRadius = Math.min(100, (entry.contentRect.width/10) + (entry.contentRect.height/10)) + 'px'; } } }); resizeObserver.observe(document.querySelector('div'));
Specifications
Specification | Status | Comment |
---|---|---|
Resize Observer The definition of 'target' in that specification. |
Editor's Draft | Initial definition. |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
contentBoxSize | Chrome No support No | Edge No support No | Firefox Full support 69 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
Legend
- Full support
- Full support
- No support
- No support
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.