denoland/deno · error · TypeError

Illegal constructor

Error message

Illegal constructor

What it means

Deno.PermissionStatus is exposed as a class but is not constructible: its constructor in runtime/js/10_permissions.js requires a private illegalConstructorKey symbol that only the permissions machinery holds. `new Deno.PermissionStatus()` throws TypeError('Illegal constructor'), matching the web-platform pattern where status objects are produced solely by query/request calls.

Source

Thrown at runtime/js/10_permissions.js:100

  onchange = null;

  /** @returns {Deno.PermissionState} */
  get state() {
    return this.#status.state;
  }

  /** @returns {boolean} */
  get partial() {
    return this.#status.partial;
  }

  /**
   * @param {{ state: Deno.PermissionState, partial: boolean }} status
   * @param {unknown} key
   */
  constructor(status = null, key = null) {
    if (key != illegalConstructorKey) {
      throw new TypeError("Illegal constructor");
    }
    super();
    this.#status = status;
  }

  /**
   * @param {Event} event
   * @returns {boolean}
   */
  dispatchEvent(event) {
    let dispatched = super.dispatchEvent(event);
    if (dispatched && this.onchange) {
      FunctionPrototypeCall(this.onchange, this, event);
      dispatched = !event.defaultPrevented;
    }
    return dispatched;
  }

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Obtain real instances from the factory API: `const status = await Deno.permissions.query({ name: 'read' })` (also querySync and request)
2. In tests, stub at the API level — replace Deno.permissions.query — instead of constructing status objects
3. If you only need the shape, define a plain type: `type StatusLike = { state: Deno.PermissionState; partial: boolean }`

Example fix

// before
const status = new Deno.PermissionStatus(); // TypeError: Illegal constructor

// after
const status = await Deno.permissions.query({ name: 'read' });
console.log(status.state, status.partial);

const isPermissionStatus = (v) => v instanceof Deno.PermissionStatus;

When it happens

Trigger: `new Deno.PermissionStatus()`; `class X extends Deno.PermissionStatus { constructor() { super(); } }` (super() is invoked without the key); test code attempting to fabricate a status object.

Common situations: Unit tests that want a fixed { state, partial } shape without stubbing the API; code ported from environments where permission status is a plain data object.

Related errors

• The provided value "${desc?.name}" is not a valid permission
• Expected the second argument to assertSnapshot() to be an op
• Snapshot serializer must return a string
• Invalid port: '${maybePort}'
• Invalid port: ${maybePort}

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/14ce21d412564616. Report an issue: GitHub.