我有不同长度的多个数组，每个数组都有键值对的对象。
[{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}]
[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}]
[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]
考虑到所有数组，如何对相同日期的 totalHours 求和？
您可以先使用扩展语法创建一个数组，然后使用reduce方法来计算总和。
let a = [{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}]
let b = [{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}]
let c = [{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]
let sum = [...a, ...b, ...c].reduce((r, {date, totalHours}) => {
if(!r[date]) r[date] = totalHours;
else r[date] += totalHours;
return r;
}, {})
console.log(sum)您可以按如下方式使用reduce函数：
const x = [{ date: '2018-11-26', totalHours: 2 }, { date: '2018-11-27', totalHours: 2 }]
const sum = x.reduce((a, c) => a + c.totalHours, 0)
console.log(sum) // 4
let a = [
...[{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}],
...[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}],
...[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]
];
let result = {};
a.forEach((i) => {
result[i.date] = result[i.date] || { date: i.date, totalHours: 0 };
result[i.date].totalHours += i.totalHours;
});
result = Object.values(result)
console.log(result);