Add throw error for undefined method on plugins

js/src/carousel.js

@@ -390,10 +390,11 @@ const Carousel = (($) => {
 
         if (typeof config === 'number') {
           data.to(config)
-
-        } else if (action) {
+        } else if (typeof action === 'string') {
+          if (data[action] === undefined) {
+            throw new Error(`No method named "${action}"`)
+          }
           data[action]()
-
         } else if (_config.interval) {
           data.pause()
           data.cycle()