You can easily achieve the result using reduce

const input = [
  { id: 1, name: "aaa" },
  { id: 1, name: "bbb" },
  { id: 2, name: "ccc" },
  { id: 3, name: "ddd" },
];

const result = input.reduce((acc, curr) => {
  const objInAcc = acc.find((o) => o.id === curr.id);
  !objInAcc ? acc.push(curr) : (objInAcc.name += `, ${curr.name}`);
  return acc;
}, []);

console.log(result);

You can group data from your array by id with a reducer like so

const input = [{ id: 1, name: "aaa" }, { id: 1, name: "bbb" }, { id: 2, name: "ccc" }, { id: 3, name: "ddd" }]

const groupedNames = input.reduce<Record<number,string[]>>((grouped, { id, name }) => (
    { ...grouped, [id]: (grouped[id] || []).concat(name) }
), {})

// then get the names as
groupedNames[id].join(', ')

// or map it to your preferred format
Object.entries(groupedNames).map(([id, names]) => ({ id, name: names.join(', ') }))