```coffeescript
module.exports = (observed, keys, callback) ->
    Object.observe observed, (changes) =>
      for change in changes
        if change.name in keys
          callback()
          break
```

Allow observing [] for all keys
user
```coffeescript
module.exports = (observed, keys, callback) ->
    Object.observe observed, (changes) =>
      for change in changes
        if (change.name in keys) or (keys.length is 0)
          callback()
          break
```
assistant