js根據對象數組中某一屬性值，合並相同項，並對某一屬性累加處理
Example: 根據code合並數組，並將sl值累加，如下兩種方法：
let data = [{ code: 1001, name: '蘋果', sl: 11 },
{ code: 1001, name: '蘋果', sl: 11 },
{ code: 1001, name: '蘋果', sl: 11 },
{ code: 1001, name: '蘋果', sl: 11 },
{ code: 1002, name: '西瓜', sl: 11 },
{ code: 1002, name: '西瓜', sl: 15 },
{ code: 1003, name: '梨', sl: 15 },
{ code: 1003, name: '梨', sl: 15 }]
第一種：根據對象key的唯一性，累加sl值
let item = {}
for (let i = 0; i < data.length; i++) {
item[data[i].code] = ~~item[data[i].code] + data[i].sl
}
console.log(item)
// 結果： {1001: 44, 1002: 26, 1003: 30}
第二種：根據reduce遍歷累加，得到數組
let newArray = data.reduce((total, cur, index) => {
let hasValue = total.findIndex(current => { return current.code === cur.code})
hasValue === -1 && total.push(cur)
hasValue !== -1 && (total[hasValue].sl = total[hasValue].sl + cur.sl)
return total
}, [])
console.log(newArray)
// 結果： [{code: 1001, name: "蘋果", sl: 44}, {code: 1002, name: "西瓜", sl: 26}, {code: 1003, name: "梨", sl: 30}]