The Tor Browser / file revision

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 "use strict";

 module.metadata = {

   "stability": "stable"

 };

 const INVALID_HOTKEY = "Hotkey must have at least one modifier.";

 const { toJSON: jsonify, toString: stringify,

         isFunctionKey } = require("./keyboard/utils");

 const { register, unregister } = require("./keyboard/hotkeys");

 const Hotkey = exports.Hotkey = function Hotkey(options) {

   if (!(this instanceof Hotkey))

     return new Hotkey(options);

   // Parsing key combination string.

   let hotkey = jsonify(options.combo);

   if (!isFunctionKey(hotkey.key) && !hotkey.modifiers.length) {

     throw new TypeError(INVALID_HOTKEY);

   }

   this.onPress = options.onPress && options.onPress.bind(this);

   this.toString = stringify.bind(null, hotkey);

   // Registering listener on keyboard combination enclosed by this hotkey.

   // Please note that `this.toString()` is a normalized version of

   // `options.combination` where order of modifiers is sorted and `accel` is

   // replaced with platform specific key.

   register(this.toString(), this.onPress);

   // We freeze instance before returning it in order to make it's properties

   // read-only.

   return Object.freeze(this);

 };

 Hotkey.prototype.destroy = function destroy() {

   unregister(this.toString(), this.onPress);

 };