Browser support

wmkit ships ES2022 (target: es2022 in tsup), ESM + CJS, no polyfills and no runtime dependencies. The floor is set by the platform APIs each layer touches, not by the syntax — so the answer differs depending on how much of the package you actually import.

Supported baselines

What you import	Chrome / Edge	Safari	Firefox	Set by
core state machine, without named layouts	94	15.4	93	the ES2022 build target
core with saveLayout / getLayout / setLayout	98	15.4	94	structuredClone; older engines copy layouts through JSON, see below
attachDesktop (drag, resize, snap, keyboard, a11y)	98	15.4	94	ES2022 and structuredClone still dominate
themes/glass.css, themes/light.css	111	16.2	113	color-mix() in the snap preview
themes/retro.css	98	15.4	94	plain borders and gradients only
@surdeddd/wmkit/persist	98	15.4	94	same as core; a missing or throwing localStorage makes it a no-op
@surdeddd/wmkit/popout	98	15.4	94	a window.open popup everywhere; picture-in-picture needs Chrome/Edge 116+ or Firefox 151+
@surdeddd/wmkit/dock	98	15.4	94	same as attachDesktop; MutationObserver marks late windows

The adapters add whatever their framework requires and nothing else: React >= 18, Vue >= 3.3, Svelte >= 4, Solid >= 1.8, Angular >= 16.

The DOM APIs the controller needs — pointer capture, ResizeObserver, requestAnimationFrame — all landed years before the ES2022 target, so they never set the floor in practice.

Practical summary: the library works in every browser from early 2022 onward; importing a bundled glass theme raises that to spring 2023. Style the windows yourself and the theme row disappears entirely.

Platform APIs, and what happens without them

API	Used by	Missing behaviour
Pointer Events + setPointerCapture	src/dom/drag.ts, src/dom/resize.ts, dock separators	no drag or resize; keyboard control and the core still work
ResizeObserver	attachDesktop viewport tracking	feature-detected — the desktop is measured once at attach; call wm.setViewport() yourself when it resizes
requestAnimationFrame	pointer batching in drag and resize	required
structuredClone	named layouts in src/core/manager.ts	layouts are copied through JSON instead: functions in meta are dropped, Dates become strings and Infinity becomes null; every other core method is unaffected
Element.animate	FLIP minimize and restore ghosts	feature-detected — the animation is skipped, state still changes
Element.moveBefore	skin rebuilds in src/dom/controller.ts	feature-detected — content moves with append, so an iframe inside a rebuilt window reloads (Chromium 133+ keeps it running)
matchMedia	coarse-pointer and reduced-motion detection	feature-detected — falls back to fine-pointer defaults
localStorage	persist default storage	read inside a try/catch; the plugin becomes a no-op, or pass your own storage
reportError	persist errors when there is no onError	feature-detected — the error is dropped silently
CSSStyleSheet.replaceSync (constructable stylesheets)	<wm-desktop>.styles, shadow skins from @surdeddd/wmkit/chrome	<wm-desktop>.styles skips CSS strings (Safari before 16.4); a shadow skin falls back to a <style> element
document.adoptedStyleSheets	popout style copying	guarded — only document.styleSheets are copied
documentPictureInPicture	popout (target: 'pip', and 'auto' when present)	'auto' falls back to a popup; isPopoutSupported('pip') returns false
window.open	popout (target: 'window')	isPopoutSupported() returns false when neither kind exists; popout() rejects with a clear error
getScreenDetails (Window Management API)	popout screen option, listScreens()	feature-detected — the popup opens at the browser's default position and listScreens() resolves null; the same happens when the permission is denied

Nothing in src/core touches window or document, so the manager can be created, mutated, serialized and hydrated during SSR. Only attachDesktop and the adapters' bind helpers need a document — call them after mount.

CSS features in the bundled themes

Feature	Where	Fallback
color-mix()	snap preview fill and border (glass.css, light.css)	the preview renders unstyled; override [data-wm-snap-preview] with a static colour
backdrop-filter	window and titlebar blur	degrades to a flat translucent panel
contain: layout style	window element	a perf hint only
individual translate / scale properties	open and modal-blocked keyframes	the animation is skipped
prefers-reduced-motion	every theme	fewer animations, never more

All themes are pure custom properties over data-wm-* attributes, so replacing a theme with your own CSS removes every requirement in this table.

Tested matrix

CI runs the full end-to-end suite on every push against:

• Chromium (Playwright Desktop Chrome)
• Firefox (Playwright Desktop Firefox)
• WebKit (Playwright Desktop Safari)
• Mobile Chromium (Playwright Pixel 7, touch and coarse pointer)

Unit tests run in Node, with jsdom for the adapter and DOM smoke tests.

Touch and pointer

Coarse pointers (pointer: coarse) automatically get larger resize hit areas (16 px edges, 24 px corners instead of 8 and 12), a wider snap threshold (20 px instead of 12), bigger snap corners (96 px instead of 64) and a 12 px magnetism threshold instead of 8. Override any of it through hitAreas, snap and magnetism in attachDesktop.

Titlebar context menus fire on right click and on long press, so onTitlebarContextMenu works the same on both input types.

Known gaps

• popout opens a popup in every engine; picture-in-picture exists in Chrome and Edge 116+ and Firefox 151+, on desktop only. Check isPopoutSupported() before showing the control, since a browser can disable both.
• Without structuredClone named layouts go through a JSON copy, which drops functions and turns Dates into strings. Keep meta and extensions JSON-safe, ship a polyfill, or store serialize() output yourself.
• Visual regression baselines are generated on macOS and skipped in CI, so rendering differences are caught by hand, not by the pipeline.