JavaScript/TypeScript: count duplicate Objects in an Array of Objects to have an amount property on Item

So I have an array of items. There are duplicate items in that array and I am trying to count these duplicates. The count of those duplicates should be put into one of the duplicate items and the other item should be discarded.

My input:

(simplified)

[
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "pickaxe",
    "emoji": "⛏️",
    "description": "Used to go mining.",
    "category": "mining",
  },
],

What I'm looking for:

[
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
    "amount": 2
  },
  {
    "id": "pickaxe",
    "emoji": "⛏️",
    "description": "Used to go mining.",
    "category": "mining",
    "amount": 1
  },
]

What I tried so far:

I have tried a few things but couldn't get there.

I've only gotten so far that I was able to only get the Item Id and the count. That looked a like this:

const itemsArray = items.map((i) => i.id); // items being my input array (see top of this post)
const itemsUnique = [...new Set(itemsArray)];
const itemsCount = itemsUnique.map((item) => [item, itemsArray.filter((i) => i === item).length])

Output:

[
  [ "fishing_rod", 2 ],
  [ "pickaxe", 1 ],
]

But that's not really what I am looking for...
A little help would be appreciated. <3

Simply iterate over and group those with the same id:

(A terser version can be found in the snippet below.)

function mergeItems(items) {
  const grouped = items.reduce((record, item) => {
    if (Object.hasOwn(record, item.id)) {
      record[item.id].count++;
    } else {
      record[item.id] = { ...item, count: 1 };
    }
    return record;
  }, {});
  return Object.values(grouped);
}

Try it:

<!-- begin snippet: js hide: true console: false babel: false -->

<!-- language: lang-js -->

console.config({ maximize: true });

function mergeItems(items) {
  const grouped = items.reduce((record, item) => {
    record[item.id] ??= { ...item, count: 0 };
    record[item.id].count++;
    return record;
  }, {});
  return Object.values(grouped);
}

const input = [
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "pickaxe",
    "emoji": "⛏️",
    "description": "Used to go mining.",
    "category": "mining",
  },
];

console.log(mergeItems(input));

<!-- language: lang-html -->

<script src="https://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

<!-- end snippet -->

We can use filter to remove the duplicates, at the same time incrementing the count.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const input = [{"id": "fishing_rod","emoji": "🎣","description": "Used to go fishing.","category": "fishing",},{"id": "fishing_rod","emoji": "🎣","description": "Used to go fishing.","category": "fishing",},{"id": "pickaxe","emoji": "⛏️","description": "Used to go mining.","category": "mining",}]

const output = input.filter((val, i, arr) => {
  const first = arr.findIndex(({ id }) => val.id === id)
  if(first === i)
    return val.amount = 1 // the current value is the first occurence
  else arr[first].amount++ // the current value is not the first occurence
})

console.log(output)

<!-- end snippet -->

Technically a one-liner

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const source = [
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "fishing_rod",
    "emoji": "🎣",
    "description": "Used to go fishing.",
    "category": "fishing",
  },
  {
    "id": "pickaxe",
    "emoji": "⛏️",
    "description": "Used to go mining.",
    "category": "mining",
  },
];

const result = {};
source.forEach((item) => result[item.id] ? result[item.id].amount ++ : result[item.id] = { ...item, amount: 1});
console.log(Object.values(result));

<!-- end snippet -->