Add hasOwnProperty check

src/js/easymde.js

@@ -239,9 +239,11 @@ function createToolbarButton(options, enableActions, enableTooltips, shortcuts,
 
     if (options.attributes) {
         for (var attribute in options.attributes) {
+            if (Object.prototype.hasOwnProperty.call(options.attributes, attribute)) {
                 el.setAttribute(attribute, options.attributes[attribute]);
             }
         }
+    }
 
     if (options.noDisable) {
         el.classList.add('no-disable');