add flipcard feature into ox-reveal

scripts/flipcard/flipcard.js

@@ -0,0 +1,31 @@
+function flipcard_main() {
+  var cardFront = document.getElementsByClassName("fc-thefront");
+  var i;
+  var flip;
+  for (i = 0; i < cardFront.length; i++) {
+    flip = document.createElement("div");
+    flip.appendChild(document.createTextNode("flip"));
+    flip.className = "fc-flip";
+    flip.addEventListener("mouseover", event => {
+      var flip = event.target;
+      var front = flip.parentElement;
+      var card = front.parentElement;
+      card.style.transform = "rotateY(180deg)";
+    });
+    cardFront[i].appendChild(flip);
+  };
+
+  var cardBack = document.getElementsByClassName("fc-theback");
+  var i;
+  for (i = 0; i < cardBack.length; i++) {
+    cardBack[i].addEventListener("mouseleave", flipcard_mouseLeave, true);
+  }
+};
+function flipcard_mouseLeave(event) {
+  if (event.target.className == "fc-theback") {
+    var back = event.target;
+    var card = back.parentElement;
+    card.style.transform = "rotateY(0deg)";
+  }
+};
+flipcard_main();