Use 0 as a fallback value instead of -1

core/source/Dom.mint

@@ -595,23 +595,29 @@ module Dom {
   Returns the distance from the outer border of the element (including its
   margin) to the left padding edge of the closest positioned ancestor element.
 
+  If the element is not in the DOM or not an element is passed (for example
+  `TextNode`) then the value will be `0`.
+
     if let Just(div) = Document.getElementBySelector("div") {
       Dom.offsetLeft(div)
     }
   */
   fun offsetLeft (element : Dom.Element) : Number {
-    `#{element}.offsetLeft || -1`
+    `#{element}.offsetLeft || 0`
   }
 
   /*
   Returns the distance from the outer border of the element (including its
   margin) to the top padding edge of the closest positioned ancestor element.
 
+  If the element is not in the DOM or not an element is passed (for example
+  `TextNode`) then the value will be `0`.
+
     if let Just(div) = Document.getElementBySelector("div") {
       Dom.offsetTop(div)
     }
   */
   fun offsetTop (element : Dom.Element) : Number {
-    `#{element}.offsetTop || -1`
+    `#{element}.offsetTop || 0`
   }
 }