# useIsMobile

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

## Signature

```ts
function useIsMobile(mobileBreakpoint?: number): boolean;
```

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

## Usage

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

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

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

## Notes

- 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'`).