Nullify props on removal (#12)

Author: natefaubion

src/Halogen/VDom/DOM/Prop.purs

@@ -189,4 +189,5 @@ unsafeGetProperty ∷ Fn.Fn2 String DOM.Element PropValue
 unsafeGetProperty = Util.unsafeGetAny
 
 removeProperty ∷ ∀ eff. Fn.Fn2 String DOM.Element (Eff (dom ∷ DOM | eff) Unit)
-removeProperty = Util.unsafeDeleteAny
+removeProperty = Fn.mkFn2 \key el →
+  Fn.runFn3 Util.unsafeSetAny key Util.jsUndefined el

src/Halogen/VDom/Util.js

@@ -184,3 +184,5 @@ exports.removeEventListener = function (ev, listener, el) {
     el.removeEventListener(ev, listener, false);
   };
 };
+
+exports.jsUndefined = void 0;

src/Halogen/VDom/Util.purs

@@ -28,6 +28,8 @@ module Halogen.VDom.Util
   , removeAttribute
   , addEventListener
   , removeEventListener
+  , JsUndefined
+  , jsUndefined
   ) where
 
 import Prelude
@@ -167,3 +169,7 @@ foreign import addEventListener
 
 foreign import removeEventListener
   ∷ ∀ eff. Fn.Fn3 String (DOM.EventListener (dom ∷ DOM | eff)) DOM.Element (Eff (dom ∷ DOM | eff) Unit)
+
+foreign import data JsUndefined ∷ *
+
+foreign import jsUndefined ∷ JsUndefined