Class ClientSettings

Register a client setting

game.settings.register("myModule", "myClientSetting", {
  name: "Register a Module Setting with Choices",
  hint: "A description of the registered setting and its behavior.",
  scope: "client",     // This specifies a client-stored setting
  config: true,        // This specifies that the setting appears in the configuration view
  requiresReload: true // This will prompt the user to reload the application for the setting to take effect.
  type: String,
  choices: {           // If choices are defined, the resulting setting will be a select menu
    "a": "Option A",
    "b": "Option B"
  },
  default: "a",        // The default value for the setting
  onChange: value => { // A callback function which triggers when the setting is changed
    console.log(value)
  }
});

Register a world setting

game.settings.register("myModule", "myWorldSetting", {
  name: "Register a Module Setting with a Range slider",
  hint: "A description of the registered setting and its behavior.",
  scope: "world",      // This specifies a world-level setting
  config: true,        // This specifies that the setting appears in the configuration view
  requiresReload: true // This will prompt the GM to have all clients reload the application for the setting to
                       // take effect.
  type: Number,
  range: {             // If range is specified, the resulting setting will be a range slider
    min: 0,
    max: 100,
    step: 10
  }
  default: 50,         // The default value for the setting
  onChange: value => { // A callback function which triggers when the setting is changed
    console.log(value)
  }
});

Define a settings submenu which handles advanced configuration needs

game.settings.registerMenu("myModule", "mySettingsMenu", {
  name: "My Settings Submenu",
  label: "Settings Menu Label",      // The text label used in the button
  hint: "A description of what will occur in the submenu dialog.",
  icon: "fas fa-bars",               // A Font Awesome icon used in the submenu button
  type: MySubmenuApplicationClass,   // A FormApplication subclass which should be created
  restricted: true                   // Restrict this submenu to gamemaster only?
});

Retrieve the current setting value

game.settings.get("myModule", "myClientSetting");

Update the current value of a setting

game.settings.set("myModule", "myClientSetting", "b");