Settings

There are two ways to introduce type checking for your package's ClientSettings with the type definitions.

Declaration Merging (recommended)

By defining your settings under the global namespace ClientSettings.Values, game.settings.get and set can become typed correctly for your package.

Consider the following setting definition:

    game.settings.register('gm-screen', 'right-margin', {
      default: 4,
      type: Number,
      scope: 'world',
      config: true,
    });

In a global.d.ts (or similar file where you're doing declaration merging), adding a declaration like the following will type the above setting correctly:

declare global {
  namespace ClientSettings {
    interface Values {
      'gm-screen.right-margin': number;
    }
  }
}

Produces the correct type checks when registering, setting, and getting the setting.

Some tests here demonstrate the technique: https://github.com/League-of-Foundry-Developers/foundry-vtt-types/blob/main/test-d/foundry/common/abstract/document.mjs.test-d.ts#L44

ClientSettings.register parameters

ClientSettings.register is a generic type and thus accepts parameters. This will allow setting registrations to work in some cases where they don't automatically (e.g. a Number with a range has issues inferring its types with a range present at the time of this writing). To bypass this, the arguments for the generic can be passed directly.

game.settings.register<string, string, number>('some', 'numberSetting', {
      default: 4,
      type: Number,
      scope: 'world',
      range: { min: 0, max: 75, step: 5 },
      config: true,
})

Note that if this is done, the setting's type is unknown when geting it elsewhere. This is much less useful than properly merging your setting types with the method outlined above.