The Resize Observer API provides a performant mechanism by which code can monitor an element for changes to its size, with notifications being delivered to the observer each time the size changes.
There are a whole raft of use cases for responsive design techniques (and others besides) that respond to changes in an element's size, but previously their implementations have often been hacky and/or brittle.
例如，
media queries
/
window.matchMedia
are great for updating layouts at specific points when the viewport changes sizes, but what if you want to change layout in response to a specific element's size changing, which isn't the outer container?
To achieve this, a limited solution would be to listen to changes to a suitable event that hints at the element you are interested in changing size (e.g. the window
resize event
), then figure out what the new dimensions or other features of the element after a resize using
Element.getBoundingClientRect
or
Window.getComputedStyle
，例如。
Such a solution tends to only work for limited use cases, be bad for performance (continually calling the above methods would result in a big performance hit), and often won't work when the browser window size is not changed.
The Resize Observer API provides a solution to exactly these kinds of problems, and more besides, allowing you to easily observe and respond to changes in the size of an element’s content or border box in a performant way. It provides a JavaScript solution to the often-discussed lack of element queries in the web platform.
Usage is simple, and pretty much the same as other observers, such as
Performance Observer
or
Intersection Observer
— you create a new
ResizeObserver
对象使用
ResizeObserver()
constructor, then use
ResizeObserver.observe()
to make it look for changes to a specific element's size. A callback function set up inside the constructor then runs every time the size changes, providing access to the new dimensions and allowing you to do anything you like in response to those changes.
ResizeObserver
Provides the ability to register new observers and to start and stop observing elements.
ResizeObserverEntry
Describes a single element which has been resized, identifying the element and its new size.
You find a couple of simple examples on our GitHub repo:
border-radius
with a percentage, but that quickly leads to ugly-looking elliptical corners, whereas the above solution gives you nice square corners that scale with the box size.
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.
The code will usually follow this kind of pattern (taken from resize-observer-border-radius.html):
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'));
| 规范 | 状态 | 注释 |
|---|---|---|
| 重置大小观测器 | 编者草案 | 初始定义。 |
| 桌面 | 移动 | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
ResizeObserver
|
Chrome 64 | Edge 79 | Firefox 69 | IE No | Opera 51 | Safari 13.1 | WebView Android 64 | Chrome Android 64 | Firefox Android No | Opera Android 47 | Safari iOS 13.4 | Samsung Internet Android 9.0 |
ResizeObserver()
构造函数
|
Chrome 64 | Edge 79 | Firefox 69 | IE No | Opera 51 | Safari 13.1 | WebView Android 64 | Chrome Android 64 | Firefox Android No | Opera Android 47 | Safari iOS 13.4 | Samsung Internet Android 9.0 |
disconnect
|
Chrome 64 | Edge 79 | Firefox 69 | IE No | Opera 51 | Safari 13.1 | WebView Android 64 | Chrome Android 64 | Firefox Android No | Opera Android 47 | Safari iOS 13.4 | Samsung Internet Android 9.0 |
observe
|
Chrome 64 | Edge 79 | Firefox 69 | IE No | Opera 51 | Safari 13.1 | WebView Android 64 | Chrome Android 64 | Firefox Android No | Opera Android 47 | Safari iOS 13.4 | Samsung Internet Android 9.0 |
unobserve
|
Chrome 64 | Edge 79 | Firefox 69 | IE No | Opera 51 | Safari 13.1 | WebView Android 64 | Chrome Android 64 | Firefox Android No | Opera Android 47 | Safari iOS 13.4 | Samsung Internet Android 9.0 |
完整支持
不支持