This is wrong. 

```js
var div = document.createElement("div"); 
div.setAttribute("data-Foo", 1); 
(div.dataset.foo === "1") === true;
```

data-* properties are always lower cased and all values in dataset become strings (conversion per [DOMString](http://www.w3.org/TR/2012/CR-html5-20121217/infrastructure.html#domstringmap-0))