Show Keyboard Shortcut Hints While a Modifier Is Held in Lit

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. HotkeyHintController has a value that's true while the user holds modifiers that belong to a hotkey. It's an optional helper, and it doesn't register anything, so use it alongside @hotkey or HotkeyController.

Show a hint next to a button#

import { LitElement, html } from 'lit'
import { customElement } from 'lit/decorators.js'
import {
  HotkeyHintController,
  formatForDisplay,
  hotkey,
} from '@tanstack/lit-hotkeys'

const saveHotkey = 'Mod+S'

@customElement('save-button')
class SaveButton extends LitElement {
  private hint = new HotkeyHintController(this, saveHotkey)

  @hotkey(saveHotkey)
  save() {
    /* ... */
  }

  render() {
    return html`
      <button @click=${() => this.save()}>
        Save ${this.hint.value ? html`<kbd>${formatForDisplay(saveHotkey)}</kbd>` : ''}
      </button>
    `
  }
}

The controller requests an update only when the hint appears or disappears. 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.

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

private hint = new HotkeyHintController(this, 'Alt+Shift+[KeyK]', { exact: true }) // Needs Alt and Shift

If the hotkey sets platform, pass the same platform to the controller, so Mod resolves the same way. The hotkey and the options can also be getters that read the element's properties.

Hints for sequences#

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

private hint = new HotkeyHintController(this, ['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 element keeps every button's hint the same:

import { LitElement, html } from 'lit'
import { customElement, property } from 'lit/decorators.js'
import {
  AppHotkeysController,
  HotkeyHintController,
  formatForDisplay,
} from '@tanstack/lit-hotkeys'
import type { AppHotkeyId } from '@tanstack/lit-hotkeys'

@customElement('shortcut-hint')
class ShortcutHint extends LitElement {
  @property() hotkeyId!: AppHotkeyId
  private app = new AppHotkeysController(this)
  private hint = new HotkeyHintController(this, () => this.app.appHotkeys[this.hotkeyId])

  render() {
    const { hotkey } = this.app.appHotkeys[this.hotkeyId]
    return this.hint.value && hotkey ? html`<kbd>${formatForDisplay(hotkey)}</kbd>` : ''
  }
}

html`<button @click=${this.save}>Save <shortcut-hint hotkeyId="doc.save"></shortcut-hint></button>`

Hide hints for hotkeys that can't fire#

HotkeyHintController only looks at held keys. It doesn't know whether the hotkey is enabled, its scope is active, or its target has focus. When a hotkey can be off, combine the hint with the same state:

@property({ type: Boolean }) dirty = false
private hint = new HotkeyHintController(this, saveHotkey)

constructor() {
  super()
  this.addController(
    new HotkeyController(this, saveHotkey, () => this.save(), () => ({
      enabled: this.dirty,
    })),
  )
}

render() {
  const showHint = this.hint.value && this.dirty
  // ...
}

Check held modifiers without the controller#

To check outside an element, such as while drawing on a canvas, pass the held keys to matchesHeldModifiers. It takes the same options:

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

const tracker = getKeyStateTracker()

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

Held Key State Helpers covers the tracker and the other held-key controllers.

The Kitchen Sink example shows hints next to its buttons while Alt or Option is held.