Show Keyboard Shortcut Hints While a Modifier Is Held in Preact

Some apps show each button's shortcut only while the user holds a modifier, so the hints are there when the user reaches for the keyboard, and out of the way otherwise. useHotkeyHint returns true while the user holds modifiers that belong to a hotkey that can fire. It's an optional helper, and it doesn't register anything, so use it alongside useHotkey.

Show a hint next to a button

tsx

import {
  formatForDisplay,
  useHotkey,
  useHotkeyHint,
} from '@tanstack/preact-hotkeys'

const saveHotkey = 'Mod+S'

function SaveButton() {
  useHotkey(saveHotkey, save)
  const showHint = useHotkeyHint(saveHotkey)

  return (
    <button onClick={save}>
      Save {showHint && <kbd>{formatForDisplay(saveHotkey)}</kbd>}
    </button>
  )
}

While the user holds Command on macOS, or Control elsewhere, the button reads "Save ⌘ S" or "Save Ctrl+S". Formatting & Display covers labels and keycaps.

When a hint shows

Holding any of the hotkey's modifiers shows the hint. For Alt+Shift+[KeyK], holding Alt, Shift, or both shows it.
Holding a modifier the hotkey doesn't use hides the hint, so holding Control and Alt shows only the hints for hotkeys that use both.
Releasing every modifier, or the window losing focus, hides the hint.
Other held keys don't matter. AltGr never shows hints, because it types characters.
A hotkey without modifiers, such as Escape or G, never shows a hint.
The hotkey must be able to fire. A hint shows only while a registration of the hotkey is enabled and in an active scope. A hotkey that nothing registers never shows a hint.
Every registration of the hotkey counts, not only the one in your component. If two components register the same hotkey and only one is enabled, both show the hint.
A hotkey bound to an element's target shows its hint only while focus is inside that element. A hotkey on document or window shows it wherever focus is.

To show a hint only while every modifier is held, pass exact:

tsx

const showHint = useHotkeyHint('Alt+Shift+[KeyK]', { exact: true }) // Needs Alt and Shift

If the hotkey sets platform, pass the same platform to useHotkeyHint, so Mod resolves the same way.

Hints for sequences

A sequence shows its hint while the user holds the modifiers of its first step:

tsx

const showHint = useHotkeyHint(['Mod+K', 'Mod+C']) // true while Mod is held

Hints for app hotkeys

Pass an app hotkey to show the user's current hotkey, including one they changed. An app hotkey with no hotkey assigned shows no hint. A small component keeps every button's hint the same:

tsx

import {
  formatForDisplay,
  useAppHotkeys,
  useHotkey,
  useHotkeyHint,
} from '@tanstack/preact-hotkeys'
import type { AppHotkeyId } from '@tanstack/preact-hotkeys'

function Hint({ id }: { id: AppHotkeyId }) {
  const appHotkey = useAppHotkeys()[id]
  const showHint = useHotkeyHint(appHotkey)

  return showHint && appHotkey.hotkey ? (
    <kbd>{formatForDisplay(appHotkey.hotkey)}</kbd>
  ) : null
}

function Toolbar() {
  useHotkey(useAppHotkeys()['doc.save'], save)

  return (
    <button onClick={save}>
      Save <Hint id="doc.save" />
    </button>
  )
}

Check held modifiers without the hook

To check outside a component, such as while drawing on a canvas, pass the held keys to matchesHeldModifiers. It takes the same options, but it only looks at held keys. To also check that the hotkey can fire, call hasActiveRegistration on the hotkey manager:

import {
  getHotkeyManager,
  getKeyStateTracker,
  matchesHeldModifiers,
} from '@tanstack/preact-hotkeys'

const tracker = getKeyStateTracker()

matchesHeldModifiers('Mod+S', tracker.getHeldKeys()) // true while Mod is held

const showHint =
  matchesHeldModifiers('Mod+S', tracker.getHeldKeys()) &&
  getHotkeyManager().hasActiveRegistration('Mod+S') // Same check as the hook