Rename private attribute _element to _el

Change-Id: I9c7a31bd6844636737ffa6456562b997f5e370a3
diff --git a/dev/js/src/hint/lengthField.js b/dev/js/src/hint/lengthField.js
index 79c7b7d..7cf8c19 100644
--- a/dev/js/src/hint/lengthField.js
+++ b/dev/js/src/hint/lengthField.js
@@ -15,12 +15,12 @@
      * Override the prefix action.
      */
     add : function (param) {
-      this._element.addE('span').addT(param[0] + '--');
+      this._el.addE('span').addT(param[0] + '--');
 
-      var desc = this._element.addE('span');
+      var desc = this._el.addE('span');
       desc.classList.add("desc");
       desc.addT(param[2] + '--');
-      this._element.appendChild(desc);
+      this._el.appendChild(desc);
     }
   };
 });