递归遍历

数据加和，使用递归遍历，对任何的子嵌套都有用

let company = { 
  sales: [{name: 'John', salary: 1000}, {name: 'Alice', salary: 600 }],
  development: {
                sites: [{name: 'Peter', salary: 2000}, {name: 'Alex', salary: 1800 }],
                internals: [{name: 'Jack', salary: 1300   }]
  }
};
//用来完成工作的函数
function sumSalaries(department) {
    if (Array.isArray(department)) {
               //prev  加和后的值，    current当前值
        return department.reduce((prev, current) => prev + current.salary, 0);  //求数组的和
    } else {
        let sum = 0;
        for (let subdep of Object.values(department)) {
                 //Object.values   取对象的值
            sum += sumSalaries(subdep);     //递归调用子对象，对结果求和
        }
        return sum;
    }
}
alert(sumSalaries(company));    //6700