Libs-Actonate

//Pass the orderItems array that you get  
  getDataArray(arr) {
    const uniqByArr = uniqBy(arr, 'item_id');
    let finalArr = [];
    uniqByArr.map((item,idx) => {
      const item_id = item.item_id;
      let qty = 0;
      arr.map((actualItem) => {
        if (item_id === actualItem.item_id) {
          qty += 1;
        }
      })
      const obj = {...item};
      obj.quantity = qty;
      finalArr.push(obj);
    })
    return finalArr;
  }