onDocumentSize

onDocumentSize(fn) registers a callback invoked with the current { width, height } whenever the viewport size changes. It is the callback half of the shared viewport Emitter whose accessor half is useDocumentSize; all subscribers share a single window resize listener. The emitter is seeded with documentSize, so the callback also fires once with the initial value. Part of pota/use/resize.

Arguments

Argument	Type	Description
fn	(size: { width: number, height: number }) => void	Called with the viewport size on change.

Examples

Log the viewport on resize

Registers a callback that fires with the initial size and again on every window resize.

import { render, signal } from 'pota'
import { onDocumentSize } from 'pota/use/resize'

function App() {
	const size = signal('resize the window')

	onDocumentSize(({ width, height }) => {
		size.write(`viewport: ${width} × ${height}`)
	})

	return <p>{size.read}</p>
}

render(App)