Add throw error for undefined method on plugins

js/src/dropdown.js

@@ -143,6 +143,9 @@ const Dropdown = (($) => {
         }
 
         if (typeof config === 'string') {
+          if (data[config] === undefined) {
+            throw new Error(`No method named "${config}"`)
+          }
           data[config].call(this)
         }
       })