使用array.reduce（）获取对象数组中对象出现次数的JavaScript代码

Question

var developers = [
    { name: "Joe", age: 23 ,overallLevel: "high"},
    { name: "Sue", age: 28 ,overallLevel: "advanced" },
    { name: "Jon", age: 32 ,overallLevel: "high" },
    { name: "Bob", age: 24 ,overallLevel: "high" },
    { name: "Bob", age: 20 ,overallLevel: "advanced" }
]

使用array.reduce（）在所提到的数组中需要计数overallLevel  [高：3，高级：2]

Answer 1

你可以用对象计算它们。

{{1}}

Answer 2

试试这个（你不需要array.reduce()来做）：

var
  i,
  count = {high: 0, advanced: 0},
  developers = [
    { name: "Joe", age: 23 ,overallLevel: "high"},
    { name: "Sue", age: 28 ,overallLevel: "advanced" },
    { name: "Jon", age: 32 ,overallLevel: "high" },
    { name: "Bob", age: 24 ,overallLevel: "high" },
    { name: "Bob", age: 20 ,overallLevel: "advanced" }
  ];

for (i in developers) {

  count[developers[i].overallLevel]++;
}

alert(JSON.stringify(count)); //  Object { high=3,  advanced=2}