获取平均年龄

编写 getAverageAge(users) 函数，该函数获取一个具有 age 属性的对象数组，并返回平均年龄。

平均值的计算公式是 (age1 + age2 + ... + ageN) / N。

例如：

          let john = { name: "John", age: 25 };
let pete = { name: "Pete", age: 30 };
let mary = { name: "Mary", age: 29 };

let arr = [ john, pete, mary ];

alert( getAverageAge(arr) ); // (25 + 30 + 29) / 3 = 28
        

function getAverageAge(users) {
  return users.reduce((prev, user) => prev + user.age, 0) / users.length;
}

let john = { name: "John", age: 25 };
let pete = { name: "Pete", age: 30 };
let mary = { name: "Mary", age: 29 };

let arr = [ john, pete, mary ];

alert( getAverageAge(arr) ); // 28