denoland/deno · warning · TypeError

Notification.requestPermission: not supported by this platfo

Error message

Notification.requestPermission: not supported by this platform/backend

What it means

Notification.requestPermission() asks the OS/backend via op_desktop_request_notification_permission. When the backend reports 'unsupported' (this OS has no notification permission model), the wrapper throws instead of answering with a misleading 'granted' or 'denied'.

Source

Thrown at cli/rt/desktop.rs:575

        get() { return cachedNotificationPermission; },
        enumerable: true,
        configurable: true,
      },
      maxActions: internals.core.propReadOnly(0),
      requestPermission: internals.core.propWritable(function requestPermission(
        cb,
      ) {
        // The Web Notifications spec gates `requestPermission` on a
        // transient user activation. The desktop runtime can't observe
        // renderer activations cleanly (the OS-level UN dialog lives
        // outside Chromium's activation tracking), so we don't enforce.
        const promise = (async () => {
          const s = await op_desktop_request_notification_permission();
          if (s === "unsupported") {
            // Honest signaling: this OS / backend has no notification
            // permission model. Throw rather than silently returning a
            // misleading "denied" or "granted".
            throw new TypeError(
              "Notification.requestPermission: not supported by this platform/backend",
            );
          }
          const perm = laufeyToNotificationPermission(s);
          cachedNotificationPermission = perm;
          return perm;
        })();
        if (typeof cb === "function") {
          // Deprecated callback form. Per spec, the callback is invoked
          // with the resolved permission *and* the promise still resolves.
          promise.then(
            (perm) => { try { cb(perm); } catch (_) {} },
            () => { try { cb("denied"); } catch (_) {} },
          );
        }
        return promise;
      }),
    });

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Wrap the call in try/catch and degrade gracefully (disable notifications).
2. Feature-detect first via Notification.permission or navigator.permissions.query({ name: 'notifications' }).
3. Confirm the desktop runtime backend supports notifications on the target OS.

Example fix

// before
const perm = await Notification.requestPermission();
// after
let perm = 'denied';
try {
  perm = await Notification.requestPermission();
} catch {
  // platform has no notification permission model
}

try {
  const perm = await Notification.requestPermission();
} catch (err) {
  if (err instanceof TypeError && /not supported/.test(err.message)) {
    notificationsEnabled = false; // unsupported platform, degrade
  } else {
    throw err;
  }
}

When it happens

Trigger: Calling Notification.requestPermission() (promise form or the deprecated callback form) on a desktop runtime OS/backend that has no notification permission model.

Common situations: Running the desktop runtime on an OS without a notification permission concept, or a build whose notification backend is absent; feature-detection code that assumes the promise always resolves.

Related errors

• Failed to execute 'query' on 'Permissions': descriptor requi
• Failed to construct 'Notification': 1 argument required, but
• Unexpected 'name' field in options, bench name is already pr
• The bench function must have a name
• Unexpected second argument to Deno.bench()

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/3e6570b7bc6b03df. Report an issue: GitHub.