helpers-ts-3.ts

function Strictly<T extends { [key: string]: Values }, Values extends string | number, O extends {}>(target: T, augmentations?: O) {
  return Object.assign(target, augmentations)
}

// for example when building a prototype object
const defaultConfig = Strictly(
  {
    state: 'MO', // "MO", not string
    settingType: 'state-settings'
  }, {
    branding: Strictly({
      type: 'header',
      color: colors.green,
      width: 500
    })
  });

defaultConfig.branding.type; // "header", not string
defaultConfig.branding.width; // 500, not number