Rename private attribute _element to _el

Change-Id: I9c7a31bd6844636737ffa6456562b997f5e370a3
diff --git a/dev/js/src/hint/prefix.js b/dev/js/src/hint/prefix.js
index 197e36e..5a83284 100644
--- a/dev/js/src/hint/prefix.js
+++ b/dev/js/src/hint/prefix.js
@@ -15,9 +15,9 @@
      * Override the prefix action.
      */
     onclick : function () {
-      var m = this.menu();
-      var value = this.value();
-      var h = m.hint();
+      const m = this.menu();
+      const value = this.value();
+      const h = m.hint();
       m.hide();
 
       h.inputField().insert(value);