Gregt/negative viewable threshold (#28)

* Can work with negative viewability threshold.

* Offset in log remark is now VT for clarity.

* Checking for isNaN

* removed logging

Co-authored-by: Engywook2005 <greg.thorson@apartmenttherapy.com>

src/Bling.js

@@ -389,7 +389,7 @@ class Bling extends Component {
     }
 
     get viewableThreshold() {
-        return this.props.viewableThreshold >= 0
+        return !isNaN(this.props.viewableThreshold)
             ? this.props.viewableThreshold
             : Bling._config.viewableThreshold;
     }

src/utils/isInViewport.js

@@ -15,10 +15,12 @@ export default function isInViewport(el, [width, height] = [0, 0], offset = 0) {
         bottom: window.innerHeight,
         right: window.innerWidth
     };
+
     const inViewport =
         rect.bottom >= viewport.top + height * offset &&
         rect.right >= viewport.left + width * offset &&
         rect.top <= viewport.bottom - height * offset &&
         rect.left <= viewport.right - width * offset;
+
     return inViewport;
 }