reducerinos

const items = [
  {
    category: "screwdrivers",
    name: "screw1"
  },
  {
    category: "perforators",
    name: "perf1"
  },
  {
    category: "perforators",
    name: "perf2"
  },
  {
    category: "screwdrivers",
    name: "screw2",
  },
  {
    category: "screwdrivers",
    name: "screw3",
  }
]

const myCats = items.reduce((acc, item) => {
  acc[item.category] = { ammount: 0}
  return acc
}, {})


const categories = items.reduce((acc, ele) => {
  if(ele.category === Object.keys(acc).find(key => key === ele.category)) {
     acc[ele.category].ammount += 1
  }  
  return acc
}, myCats)