Js fix

restructured the js as a class and use `keyup` events to trigger count update, which's more efficient than timer callbacks.

see https://github.com/GigaOM/gigaom/issues/5767
Since `this.$title_span` is a jQuery object, it shouldn't be `undefined`. However, you could switch this to:

```js
if ( ! this.$title_span.length ) {
```