如何检查 object 的属性值？

Question

我需要找到一个属性在 object 中具有特定值的次数。

object：

let users = {
  Alan: {
    age: 27,
    online: false
  },
  Jeff: {
    age: 32,
    online: true
  },
  Ryan: {
    age: 19,
    online: true
  }
};

我需要找到多少在线有多少值为真

到目前为止我已经尝试过：

function countOnline(obj) {
  let count = 0;
    for (let user in obj) {
      if (obj.user == true) {
      count++;
      }
    }
  return count;
}

console.log(countOnline(users)); // 0
console.log(users.Ryan.online); // true

console.log(countOnline(users)); // should return 2 as the number of online: true exists twice

Answer 1

我会reduce Object.values的 Object.values，当online为真时增加累加器：

 let users = { Alan: { age: 27, online: false }, Jeff: { age: 32, online: true }, Ryan: { age: 19, online: true } }; const onlineCount = Object.values(users).reduce((a, { online }) => a + online, 0); console.log(onlineCount);

要修复现有代码，请将测试更改为obj[user].online === true （或只是obj[user].online ）：

 let users = { Alan: { age: 27, online: false }, Jeff: { age: 32, online: true }, Ryan: { age: 19, online: true } }; function countOnline(obj) { let count = 0; for (let user in obj) { if (obj[user].online === true) { count++; } } return count; } console.log(countOnline(users));

Answer 2

您需要访问obj的在线属性

if (obj[user].online == true) or if (obj[user].online)

当您执行obj.user时，它会尝试在obj上查找user属性，其值将undefined ，因为我们在obj上没有任何名为user的属性

您可以简单地根据在线属性过滤值并检查长度

 let users = {Alan: {age: 27,online: false},Jeff: {age: 32,online: true},Ryan: {age: 19,online: true}}; let count = Object.values(users).filter(({ online }) => online).length console.log(count)

Answer 3

 let users = { Alan: { age: 27, online: false }, Jeff: { age: 32, online: true }, Ryan: { age: 19, online: true } }; let onlineUser = Object.keys(users).filter(item => users[item].online).reduce((obj, key) => { obj[key] = users[key]; return obj; }, {}); console.log("count:", Object.keys(onlineUser).length); console.log("onlineUser:", onlineUser);