ts_example_4

ts_example_4.ts

function assertNever(x: never): never {
  throw new Error("Unexpected object: " + x);
}

const Message: React.FC<MessageProps> = ({ message }) => {
  switch (message.author.__typename) {
    case "User": {
      return <div style={{color: premiumColor(message.author.role)}}>{`${message.author.name}: ${message.text}`}</div>;
    }
    case "Guest": {
      return <div>{`${message.author.placeholder}: ${message.text}`}</div>;
    }
    case "%other": {
      return null;
    }
    default: {
      assertNever(message.author);
    }
  }
};

function premiumColor(role: USER_ROLE) {
  switch (role) {
    case "PREMIUM": {
      return "red";
    }
    case "FREE": {
      return "black";
    }
    case "%future added value": {
      return "black";
    }
  }
}