useOs

Import

import { useOs } from "@knitui/hooks";

Signature

export function useOs(): OS

Returns the operating system the app is running on: macos, ios, windows, android, linux, web, or undetermined when it cannot tell yet. The two platforms answer the question from completely different sources, which is why the hook is split.

On native it is Platform.OS, which is known synchronously — no state, no effect, correct on the very first render. On web there is no such API, so it matches navigator.userAgent against a short list of patterns, and it does that in a mount effect rather than during render. That is deliberate: reading navigator while rendering on the server is either impossible or wrong, and returning a real value on the first client render would make the client's markup disagree with the server's. So the first web render is always undetermined, and the real value lands on the render after mount.

When to use it

• Rendering the right shortcut hint: ⌘K on macOS, Ctrl+K elsewhere.
• Offering the correct download or install instructions.
• Copy or affordances that differ per platform, where a media query is the wrong tool.

Notes

• Handle undetermined explicitly on web. It is the value on the first render and under SSR, so branching without a fallback produces a visible flash of the wrong variant.
• Web detection is user-agent based and inherits that mechanism's limits: it sees what the browser reports, so a device sending a desktop user agent is detected as a desktop OS.
• It answers which OS, not how big the screen is or whether there is a mouse. For layout decisions use useMedia() or @knitui/mediaquery instead.