"use strict";
  
  // This mixin doesn't have an IDL equivalent, but since MouseEvent and KeyboardEvent implement getModifierState() the
  // same way, its implementation is shared here.
  
  class EventModifierMixinImpl {
    // Event's constructor assumes all options correspond to IDL attributes with the same names, and sets them on `this`.
    // That is not the case for these modifier boolean options, but since the options are set on `this` anyway we'll
    // access them that way. The spec doesn't say much about the case where keyArg is not one of the valid ones
    // (https://w3c.github.io/uievents-key/#keys-modifier), but at least Chrome returns false for invalid modifiers. Since
    // these invalid modifiers will be undefined on `this` (thus `false` after casting it to boolean), we don't need to do
    // extra checking for validity.
    getModifierState(keyArg) {
      return Boolean(this[`modifier${keyArg}`]);
    }
  }
  
  exports.implementation = EventModifierMixinImpl;