Add multiple keys with the same id

let orgArr = [
  {
    
     xid: '1q2wss', month: '02', electricity: 1 },
  {
    
     xid: '1q2wss', month: '03', electricity: 2 },
  {
    
     xid: 'wwws', month: '02', electricity: 3 },
  {
    
     xid: 'wwws', month: '03', electricity: 4 }
]

let res = []
let flag = {
    
    } // 用来判断该id是否第一次出现

for (let i in orgArr) {
    
    
  let item = orgArr[i]
  console.log(item) // 输出数组里的每条数据
  if (!flag[item.xid]) {
    
     // 第一次出现这个id
    res.push({
    
    
      xid: item.xid,
      electricity: item.electricity
    })
    flag[item.xid] = item // 出现过一次的id就放入flag里
  } else {
    
     // 非第一次出现这个id
    for (let j = 0; j < res.length; j++) {
    
     //遍历res数组，找到相同的id，进行相加
      if (res[j].xid === item.xid) {
    
    
        res[j].electricity = res[j].electricity + item.electricity
      }
    }
  }
}
console.log(res)

Output

[
 {
    
    xid: "1q2wss", electricity: 3},
 {
    
    xid: "wwws", electricity: 7}
]