ResizeObserver: observe() method
The observe()
method of the
ResizeObserver
interface starts observing the specified
Element
or SVGElement
.
Syntax
js
observe(target)
observe(target, options)
Parameters
target
-
A reference to an
Element
orSVGElement
to be observed. options
Optional-
An options object allowing you to set options for the observation. Currently this only has one possible option that can be set:
box
-
Sets which box model the observer will observe changes to. Possible values are:
content-box
(the default)-
Size of the content area as defined in CSS.
border-box
-
Size of the box border area as defined in CSS.
device-pixel-content-box
-
The size of the content area as defined in CSS, in device pixels, before applying any CSS transforms on the element or its ancestors.
Return value
None (undefined
).
Exceptions
None.
Examples
The following snippet is taken from the resize-observer-text.html (see source) example:
js
const resizeObserver = new ResizeObserver((entries) => {
for (const 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);
An observe()
call with an options object would look like so:
js
resizeObserver.observe(divElem, { box: "border-box" });
Specifications
Specification |
---|
Resize Observer # dom-resizeobserver-observe |
Browser compatibility
BCD tables only load in the browser