freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/basic-data-structures/iterate-through-the-keys-of-an-object-with-a-for...in-statement/index.md

---
title: Iterate Through the Keys of an Object with a for...in Statement
---
#  Iterate Through the Keys of an Object with a for...in Statement

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## Problem Explanation
- Note: `dot-notation` will cause errors in this challenge. 
- `[square-bracket]` notation must be used to call a variable property name.
- The following code will not work.


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## Hints

### Hint 1:

```javascript
for (let user in obj) {
  if (obj.user.online === true) {
    //code
  }
}
```

### Hint 2
- Example 2 demonstrates how using `[square-bracket]` notation the code will be executed.

```javascript
for (let user in obj) {
  if (obj[user].online === true) {
    //code
  }
}
```


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## Solutions
<details><summary>Solution 1 (Click to Show/Hide)</summary>

```javascript
let users = {
  Alan: {
    age: 27,
    online: false
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: false
  },
  Ryan: {
    age: 19,
    online: true
  }
};
function countOnline(obj) {
  // change code below this line
  let result = 0;
  for (let user in obj) {
    if (obj[user].online === true) {
      result++;
    }
  }
  return result;
  // change code above this line
}
console.log(countOnline(users));
```
</details>