npm and error messages

node_modules/vue/src/compiler/directives/on.js

@@ -0,0 +1,10 @@
+/* @flow */
+
+import { warn } from 'core/util/index'
+
+export default function on (el: ASTElement, dir: ASTDirective) {
+  if (process.env.NODE_ENV !== 'production' && dir.modifiers) {
+    warn(`v-on without argument does not support modifiers.`)
+  }
+  el.wrapListeners = (code: string) => `_g(${code},${dir.value})`
+}