Track Held Keys and Modifier State in Angular

These functions report which keys the user is holding right now. They're optional helpers for your UI: show which modifiers are down, or change a button while Shift is held. You don't need them to register hotkeys. To show a button's shortcut while the user holds its modifiers, see Hotkey Hints.

Each function returns a signal. Call them in an injection context, such as a field initializer or a constructor.

Show which keys are held

injectHeldKeys returns the held keys in the order they were pressed, such as ['Control', 'Shift', 'A']:

import { Component } from '@angular/core'
import { injectHeldKeys } from '@tanstack/angular-hotkeys'

@Component({
  selector: 'app-key-display',
  template: `
    <div>
      {{ heldKeys().length > 0 ? 'Held: ' + heldKeys().join(' + ') : 'No keys held' }}
    </div>
  `,
})
export class KeyDisplayComponent {
  readonly heldKeys = injectHeldKeys()
}

Check whether a key is held

injectKeyHold returns whether one key is held. It updates only when that key is pressed or released, and accepts a getter for a key that changes:

import { Component, input } from '@angular/core'
import { injectKeyHold } from '@tanstack/angular-hotkeys'

@Component({
  selector: 'app-file-item',
  template: `
    <span>{{ file().name }}</span>
    @if (isShiftHeld()) {
      <button (click)="permanentlyDelete(file())">Delete permanently</button>
    } @else {
      <button (click)="moveToTrash(file())">Move to trash</button>
    }
  `,
})
export class FileItemComponent {
  readonly file = input.required<File>()
  readonly isShiftHeld = injectKeyHold('Shift')
}

Tell left and right modifiers apart

injectHeldKeyCodes maps each held key to the physical key that's down, from event.code:

import { Component } from '@angular/core'
import { injectHeldKeyCodes } from '@tanstack/angular-hotkeys'

@Component({
  selector: 'app-modifier-sides',
  template: `
    @if (heldCodes()['Shift'] === 'ShiftRight') {
      <p>Right Shift is held</p>
    }
  `,
})
export class ModifierSidesComponent {
  readonly heldCodes = injectHeldKeyCodes() // e.g. { Shift: 'ShiftLeft', Control: 'ControlRight' }
}

Read held keys in an event handler

To read the held keys in an event handler without tracking them, use the shared tracker from getKeyStateTracker:

import { Component } from '@angular/core'
import { getKeyStateTracker } from '@tanstack/angular-hotkeys'

@Component({
  selector: 'app-canvas',
  template: `<canvas (click)="onClick()"></canvas>`,
})
export class CanvasComponent {
  private readonly tracker = getKeyStateTracker()

  onClick() {
    if (this.tracker.isKeyHeld('Space')) this.startPanning()
    else if (this.tracker.isAnyKeyHeld(['Shift', 'Control'])) this.addToSelection()
    else this.select()
  }
}

The tracker starts listening the first time you get it, so get it when the component is created, before the user presses the keys you care about. Call its methods inside the handler to read the state at that moment. It also has getHeldKeys() and areAllKeysHeld(keys). Don't destroy the tracker when a component is destroyed, because every function shares it.

For a mouse or wheel event, event.ctrlKey, shiftKey, altKey, and metaKey already report the modifiers. Browsers also set ctrlKey for a trackpad pinch, so it doesn't always mean Control is held.

Held keys clear when the window loses focus, so a key released after switching apps doesn't stay held. Held keys reset when the window loses focus covers the cases the tracker handles.

The injectHeldKeys example shows held keys and their codes, and the injectKeyHold example shows modifier indicators.