js数组对象的相同值相加合并

mergeArr(arr){
        var newArr=[];
          arr.forEach(item => {
          var dataItem = item;
            if(newArr.length>0) {
                var filterValue = newArr.filter(v => {
                  return v.partNo == dataItem.partNo
                })
                if(filterValue.length>0){
                    newArr.forEach(n => {
                      if( n.partNo == filterValue[0].partNo){
                          n.itemQty = filterValue[0].itemQty + dataItem.itemQty
                      } 
                    })
                }else{
                    newArr.push(dataItem)
                }
            }else{
                newArr.push(dataItem)
            }
        })
        return newArr
      }