Deprecated: use native ResizeObserver construct available in most modern browsers along with the resize-observer-polyfill if needed.

A lit and polymer compatible solution to reacting to changes in an element's size and/or position. Contains a polyfill for ResizeObserver that is able to detect changes inside of webcomponents on all supported browsers (Firefox, Chrome/Chromium, Edge, IE11, and Safari).

To use the polyfill, simply import resize-observer-polyfill.js into the page:

import '@brightspace-ui/resize-aware/resize-observer-polyfill.js';

or

<script type="module" src="@brightspace-ui/resize-aware/resize-observer-polyfill.js"></script>

Alternatively, if you do not wish to alter or define window.ResizeObserver, you can instead import the polyfill as an es6 module:

import { ResizeObserver } from '@brightspace-ui/resize-aware/resize-observer-module.js';

Additionally, a separate class is provided that is capable to detecting changes in position as well as size, and checks the client bounding box (as returned by getBoundingClientRect()) rather than its content box.

import { BoundingBoxObserver } from '@brightspace-ui/resize-aware/resize-observer-module.js';

This repo also includes a webcomponent implementing the polyfill for convenience:

<d2l-resize-aware>
  ...
</d2l-resize-aware>

• position-aware (flag) - Also fires a d2l-resize-aware-resized event when the component's position changes (by default this event is only fired on a size change)

• d2l-resize-aware-resized Fired when the component's size (or position if the position-aware flag is specified) changes. This event is also fired once when the component is attached to the DOM.

  Bubbles: no Properties:

  • target (Node) - The <d2l-resize-aware> element that fired the event
  • detail.previous (DomRect) - The previous bounding box of the element before the size changed
  • detail.current (DomRect) - The new bounding box of the element (equal to the result of target.getBoundingClientRect())

The latest version of all major browsers (including Internet Explorer) are supported.

There are 3 different implemenations that will be used depending on the browser, plus an additional workaround for Safari:

• Browser natively supports ResizeObserver (Chrome, Chromium) Simply use the native ResizeObserver, unless position-aware is specified, in which case use the 3rd implementation
• Browser supports neither ResizeObserver nor native Shadow DOM, using the Shady DOM polyfill instead (Edge, IE11) Uses a single MutationObserver plus a resize and transitionend event handler on the window, and relies on the shady DOM polyfill to detect changes in the shady DOM of webcomponents
• Browser supports native Shadow DOM, but not ResizeObserver (Firefox, Safari) Like above, but also recursively adds a MutationObserver and transitionend event listener to the shadow root of all webcomponents so that changes within the shadow DOM of webcomponents can be detected. As webcomponents are added and removed, the tree of mutation observers is automatically updated.

Safari has a browser bug that prevents the resizing of a textarea using the native resize handle from being detected by mutation observers. To work around this bug, if the browser is detected as Safari, and a textarea element whose resize styling does not resolve to none (that is, it has a drag handle) is found on the page, this component will poll for changes in size whenever the mouse is moving or a moving touch event occurs.

The polyfill and component are unable to detect changes in position or size that occur as a result of CSS pseudo-class styling (eg. :hover) unless said syling has a transition.

If the browser natively supports ResizeObserver, the BoundingBoxObserver class will use both the native ResizeObserver and the polyfill together to cover each other's limitations. A CSS pseudo-class that causes another element to move but not change size will still not be detected, however, as neither the native implementation nor the polyfill can handle this case.

This repo is configured to use semantic-release. Commits prefixed with fix: and feat: will trigger patch and minor releases when merged to main.

To learn how to create major releases and release from maintenance branches, refer to the semantic-release GitHub Action documentation.