What's the output?

Question

```javascript
const person = {
  name: 'Lydia Hallie',
  hobbies: ['coding'],
};

function addHobby(hobby, hobbies = person.hobbies) {
  hobbies.push(hobby);
  return hobbies;
}

addHobby('running', []);
addHobby('dancing');
addHobby('baking', person.hobbies);

console.log(person.hobbies);
```

Accepted Answer

The `addHobby` function receives two arguments, `hobby` and `hobbies` with the default value of the `hobbies` array on the `person` object.

First, we invoke the `addHobby` function, and pass `"running"` as the value for `hobby` and an empty array as the value for `hobbies`. Since we pass an empty array as the value for `hobbies`, `"running"` gets added to this empty array.

Then, we invoke the `addHobby` function, and pass `"dancing"` as the value for `hobby`. We didn't pass a value for `hobbies`, so it gets the default value, the `hobbies` property on the `person` object. We push the hobby `dancing` to the `person.hobbies` array.

Last, we invoke the `addHobby` function, and pass `"baking"` as the value for `hobby`, and the `person.hobbies` array as the value for `hobbies`. We push the hobby `baking` to the `person.hobbies` array.

After pushing `dancing` and `baking`, the value of `person.hobbies` is `["coding", "dancing", "baking"]`

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