如何检查 object 的属性值？

Question

I need to find the number of times a property has a specific value in an object.

The object:

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

I need to find the number of how many online have the value true

What I've tried so far:

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

I'd reduce the Object.values of the object, incrementing the accumulator when online is true:

 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);

To fix your existing code, change the test to obj[user].online === true (or just 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

You need to access online property of obj

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

When you do obj.user it tries to find user property on obj whose value will be undefined as we don't have any property named user on obj

You can simply filter values based on online property and check length

 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);