let arry=[
    {Code:'x',Quantity:1,ItemType:'normal'},
    {Code:'x',Quantity:2,ItemType:'normal'},
    {Code:'x',Quantity:5,ItemType:'normal'},
    {Code:'y',Quantity:1,ItemType:'spec'},
    {Code:'y',Quantity:2,ItemType:'spec'},
    {Code:'z',Quantity:1,ItemType:'normal'},
    ]
    let newfood=[];
    var
 
 temp = {};
        for(var i in arry) {
            var key= arry[i].Code;
            if(temp[key]) {
                temp[key].Code = temp[key].Code ;
                temp[key].Quantity = temp[key].Quantity+ arry[i].Quantity;

            } else {
                temp[key] = {};
                temp[key].Code = arry[i].Code;
                temp[key].Quantity = arry[i].Quantity;

            }
            temp[key].ItemType= arry[i].ItemType; 
        }
      for
 
(var k in temp){
         newfood.push(temp[k])
      }
      alert(JSON.stringify(newfood));