Js statistics the number of repetitions of elements in the array (b)

let list = [
　　{name: "1000 Points", the serialNumber:. 6 },
　　{name: "500 Points", the serialNumber:. 7 },
　　{name: "50 Points", the serialNumber:. 8 }, 　　{name: "50 Points", the serialNumber:. 8 }, 　　{name: "50 Points", the serialNumber:. 8 }];

How to list an array into

[ 
　　{Title: "1000 Points", num: 1},

　　{Title: "500 Points", num: 1},

　　{Title: "50 Points", num: 3}

] 
// NUM: number of repetitions of the same elements serialNumber

 

let _res = [];
for(let i = 0; i < list.length;) {
    let count = 0;
    for(let j = i; j < list.length; j++) {
        if(list[i].serialNumber == list[j].serialNumber) {
            count++;
        }
    }
    let obj = {
        title:list[i].name,
        num:count
    }
    _res.push(obj)
    i += count;
}

console.log(_res)

//[{"title":"1000积分","num":1},{"title":"500积分","num":1},{"title":"50积分","num":3}]