Javascript – TypeError: groupBy(…).map is not a function

I tried to group json data with specific key like that:

function groupBy(items) {
    return items.reduce((acc, curr) => {
      if (curr.league?.id) {
        const { id } = curr.league;
        const currentItems = acc[id];
    
        return { 
          ...acc,
          [id]: currentItems ? [...currentItems, curr] : [curr]
        };
      }
      return acc;
    }, {});
  }

    console.log(groupBy(matches))

Then I get a correct result like that

but when I tried to get data using The map() method like that :

groupBy(matches).map((match, index) => ( ..... ))

I get this error :

groupBy(...).map is not a function TypeError: groupBy(...).map is not a function

Any Idea?