add document.activeElement (#136)

* add `document.activeElement`

* Document -> HTMLDocument from the Node file

* fix Eff type signature

* remove `yarn.lock` and ignore it as well

Author: toastal

.gitignore

@@ -6,3 +6,4 @@
 /node_modules/
 /output/
 *.tix
+yarn.lock

src/DOM/HTML/Document.js

@@ -11,3 +11,9 @@ exports._readyState = function (doc) {
     return doc.readyState;
   };
 };
+
+exports._activeElement = function (doc) {
+  return function () {
+    return doc.activeElement;
+  };
+};

src/DOM/HTML/Document.purs

@@ -24,3 +24,8 @@ foreign import _readyState :: forall eff. HTMLDocument -> Eff (dom :: DOM | eff)
 
 readyState :: forall eff. HTMLDocument -> Eff (dom :: DOM | eff) ReadyState
 readyState = map (unsafePartial fromJust <<< parseReadyState) <<< _readyState
+
+foreign import _activeElement :: forall eff. HTMLDocument -> Eff (dom :: DOM | eff) (Nullable HTMLElement)
+
+activeElement :: forall eff. HTMLDocument -> Eff (dom :: DOM | eff) (Maybe HTMLElement)
+activeElement = map toMaybe <<< _activeElement