Preventing Browser Keyboard Shortcuts on WebAssembly

When running an Uno Platform Skia WebAssembly app, certain browser keyboard shortcuts (such as <kbd>Ctrl</kbd>+<kbd>S</kbd>, <kbd>F5</kbd>, or <kbd>Ctrl</kbd>+<kbd>+</kbd>/<kbd>-</kbd>) can interfere with the application by triggering browser-native actions instead of being handled by the Uno input pipeline.

The BrowserInputHelper class provides APIs to control this behavior, giving developers fine-grained control over browser zoom and keyboard lock features.

Default behavior

By default, the Uno Skia WebAssembly runtime routes keyboard events through the Uno input pipeline. When a key event is marked as Handled (either by your app or by Uno's built-in handling), preventDefault() is called on the underlying DOM event, preventing the corresponding browser shortcut from firing. This means:

• Keys like <kbd>F5</kbd> (refresh), <kbd>Ctrl</kbd>+<kbd>S</kbd> (save), and <kbd>Ctrl</kbd>+<kbd>P</kbd> (print) can be intercepted by your app when you handle those key events.
• Standard text input, clipboard operations (<kbd>Ctrl</kbd>+<kbd>C</kbd>/<kbd>V</kbd>/<kbd>X</kbd>), and other in-app keyboard interactions continue to work normally.
• Browser zoom via <kbd>Ctrl</kbd>+mouse wheel is allowed by default.

For most in-app shortcuts, no additional configuration is required beyond handling the relevant key events. For OS- or browser-reserved shortcuts (such as tab management or focusing the address bar), you may need the Keyboard Lock API described below.

Prerequisites

The BrowserInputHelper class is WebAssembly Skia-specific. It resides in the Uno.UI.Runtime.Skia namespace and is only available in the Uno.WinUI.Runtime.Skia.WebAssembly.Browser package.

When using this API, guard your code with platform checks:

#if HAS_UNO_SKIA
using Uno.UI.Runtime.Skia;
#endif

Disabling browser zoom

By default, <kbd>Ctrl</kbd>+mouse wheel triggers the browser's built-in page zoom. You can disable this so your app receives the wheel events instead (for example, to implement custom zoom-to-cursor behavior in a canvas or map control):

#if HAS_UNO_SKIA
// Disable browser zoom - Ctrl+wheel events are delivered to the Uno app instead
BrowserInputHelper.IsBrowserZoomEnabled = false;
#endif

To re-enable browser zoom:

#if HAS_UNO_SKIA
BrowserInputHelper.IsBrowserZoomEnabled = true;
#endif

Keyboard Lock API

Some system-level keys (like <kbd>Escape</kbd>, <kbd>Alt</kbd>+<kbd>Tab</kbd>, or <kbd>Meta</kbd>) are intercepted by the browser or OS before they reach the web page. The Keyboard Lock API allows you to capture even these keys.

[!IMPORTANT] The Keyboard Lock API requires HTTPS and is only supported in Chromium-based browsers (Chrome, Edge). It does not work in Firefox or Safari. The app must also be in fullscreen mode for the lock to take effect.

Checking browser support

Before calling LockKeysAsync, you can check whether the current browser supports the Keyboard Lock API:

#if HAS_UNO_SKIA
if (BrowserInputHelper.IsKeyboardLockSupported)
{
    await BrowserInputHelper.LockKeysAsync("Escape", "F11");
}
else
{
    // Fallback: Keyboard Lock API not available in this browser
}
#endif

Locking specific keys

To lock specific keys so they are delivered to your app instead of the browser or OS:

#if HAS_UNO_SKIA
// Lock Escape and F11 so they reach the Uno app
await BrowserInputHelper.LockKeysAsync("Escape", "F11");
#endif

Key codes use the KeyboardEvent.code format (e.g., "KeyW", "F5", "Escape", "MetaLeft").

Locking all keys

To lock all keys:

#if HAS_UNO_SKIA
// Lock all capturable keys
await BrowserInputHelper.LockKeysAsync();
#endif

Unlocking keys

To release all locked keys and restore default browser key handling:

#if HAS_UNO_SKIA
BrowserInputHelper.UnlockKeys();
#endif

API reference

BrowserInputHelper.IsBrowserZoomEnabled

BrowserInputHelper.IsKeyboardLockSupported

BrowserInputHelper.LockKeysAsync(params string[] keyCodes)

BrowserInputHelper.UnlockKeys()

Browser compatibility