I am trying to replace my old ID with new one but this function is not working. How can I resolve this error?

```js
$("#addfield").click(function(){
    alert($(this).data('id')+1);
    $(this).data('id', + $('#addfield').data('id')+1);
    console.log($(this).data('id'));
})
```

```html
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<a class="btn btn-success addfield" id="addfield" class="addfield" data-id="1">Add field</a>
```