减少回调函数以从数组中检索属性

Question

给定以下数组，我将编写一个回调函数以减少到 return 一个具有两个键的对象 - 'JavaScript' 和 'python'。密钥应等于使用 'JavaScript' 或 'python' 作为其语言的开发人员的数量。最终控制台日志应为 JavaScript: 4, Python:3.

const developersArray = [
    { name: 'ralph', language: 'javascript' },
    { name: 'gretchen', language: 'javascript' },
    { name: 'alice', language: 'python' },
    { name: 'mohammed', language: 'javascript' },
    { name: 'pat', language: 'python' },
    { name: 'taylor', language: 'python' },
    { name: 'hideo', language: 'javascript' },
];

到目前为止，这就是我想出的。我正在回顾一项旧作业，认为我走在正确的轨道上，但不确定我是否走对了路：

const devLanguageCounts = developersArray.reduce(() => developersArray.language === 'javascript' && 'python' ? ++developersArray : 'javascript', 'python');

非常感谢任何帮助

Answer 1

使用 forEach 的简单方法并检查 hasOwnProperty 语言是否已经存在 res 在其他地方增加它用 1 初始化它：

const developers = [
  { name: "ralph", language: "javascript" },
  { name: "gretchen", language: "javascript" },
  { name: "alice", language: "python" },
  { name: "mohammed", language: "javascript" },
  { name: "pat", language: "python" },
  { name: "taylor", language: "python" },
  { name: "hideo", language: "javascript" },
];
   
res = {};
developers.forEach(({ language }) => {
  if (res.hasOwnProperty(language)) {
    res[language] += 1;
  } else {
    res[language] = 1;
  }
});
console.log(res)

Answer 2

使用 reduce 动态使用 Logical_nullish_assignment 初始 object 如果语言不存在 0 或获取其先前的值，则递增它。

const developers = [
  { name: "ralph", language: "javascript" },
  { name: "gretchen", language: "javascript" },
  { name: "alice", language: "python" },
  { name: "mohammed", language: "javascript" },
  { name: "pat", language: "python" },
  { name: "taylor", language: "python" },
  { name: "hideo", language: "javascript" },
];
const devLanguageCounts = developers.reduce((prev, { language }) => {
  prev[language] ??= 0;
  prev[language]++;
  return prev;
}, {});
console.log(devLanguageCounts);

减少回调函数以从数组中检索属性

Reduce callback function to retrieve properties from an array

javascript

function

callback