Javascript - Counting duplicates in object array and storing the count as a new object

Question

I have an array of javascript objects that are products. These products are displayed in a list as a cart.

I want to count the number of duplicate products in the ar

Answer 1

You can make use of array.reduce method to convert an original array into a new array with desired structure. We can just check if the id exists in the array and accordingly update the array with new object having count property.

let arr = [{
  id: 1
}, {
  id: 1
}, {
  id: 1
}, {
  id: 2
}, {
  id: 2
}];

let new_arr = arr.reduce((ar, obj) => {
  let bool = false;
  if (!ar) {
    ar = [];
  }
  ar.forEach((a) => {
    if (a.id === obj.id) {
      a.count++;
      bool = true;
    }
  });
  if (!bool) {
    obj.count = 1;
    ar.push(obj);
  }
  return ar;
}, []);

console.log(new_arr);