Dealing with key value pairs

type Stats = {
  max: {
    [key: string]: number;
  };
  sum: {
    [key: string]: number;
  };
  mean: number;
};

type Stats = {
  max: {
    [key: string]: number;
  };
  sum: {
    [key: string]: number;
  };
  mean: number;
};