useIsMobile

Returns true when the viewport width is below a configurable breakpoint, and re-evaluates reactively on resize.

Signature

function useIsMobile(mobileBreakpoint?: number): boolean;

Parameter	Type	Default	Description
`mobileBreakpoint`	`number`	`1024`	Viewport width (px) at which the device is considered mobile

function Navbar() {
  const isMobile = useIsMobile();

  return isMobile ? <MobileNav /> : <DesktopNav />;
}

// Custom breakpoint
const isTablet = useIsMobile(768);

Uses window.matchMedia for the resize listener (more efficient than resize event polling).
Returns false during SSR (initial state is undefined, coerced via !!).
Client-only ('use client').