What?

Follow up to #76446.

Make useMediaQuery and useViewportMatch safe to call during server-side rendering. Today they throw ReferenceError: window is not defined the moment they're invoked under Node SSR or a jest-environment node test, unmounting the whole React tree.

Why?

#76446 added an optional view: Window argument to both hooks, defaulting to the global window:

const useViewportMatch = ( breakpoint, operator = '>=', view = window ) => { … }

export default function useMediaQuery(
    query?: string,
    view: Window = window
): boolean { … }

Default parameter expressions are evaluated unconditionally at every call. In a non-DOM environment, window is an unbound identifier, so the bare reference throws a ReferenceError before the function body ever runs — and the existing SSR-safe machinery inside the body (useSyncExternalStore(subscribe, getValue, () => false), with
() => false as the server snapshot) never gets a chance to execute.

How?

• Resolve the view default lazily inside the parameter list with typeof window !== 'undefined' ? window : undefined. The default expression itself is now safe, and consumers passing an explicit view are unaffected.
• Widen getMQLSubscriber's signature to accept Window | undefined and short-circuit to EMPTY_SUBSCRIBER when view is falsy, so the type matches the new reality and WeakMap.get(undefined) is impossible.

With these changes, SSR renders fall through to the useSyncExternalStore server snapshot and produce false; the real match is computed on the client after mount, as before.

Test coverage

Adds a regression test under @jest-environment node that renders both hooks via react-dom/server's renderToString. Without the fix, all three cases throw the original ReferenceError.

To make a Node-environment test runnable under the shared Jest config, the jsdom-only setup in packages/jest-preset-default/scripts/setup-globals.js and test/unit/{config,mocks} is guarded with typeof window !== 'undefined'. The @testing-library/user-event mock stays at the module top level (needed for babel-jest hoisting) and falls back to a passthrough when there is no DOM.

Use of AI Tools

Authored with assistance from Claude Code (Opus 4.7). All changes were reviewed and tested by the author.