Merge pull request #1515 from storybooks/addon-channel-warning

Addon channel warning

app/react-native/src/preview/index.js

@@ -55,7 +55,15 @@ export default class Preview {
   getStorybookUI(params = {}) {
     return () => {
       let webUrl = null;
-      let channel = addons.getChannel();
+      let channel = null;
+
+      try {
+        channel = addons.getChannel();
+      } catch (e) {
+        // getChannel throws if the channel is not defined,
+        // which is fine in this case (we will define it below)
+      }
+
       if (params.resetStorybook || !channel) {
         const host = params.host || parse(NativeModules.SourceCode.scriptURL).hostname;
         const port = params.port !== false ? `:${params.port || 7007}` : '';

lib/addons/src/index.js

@@ -2,15 +2,19 @@ export class AddonStore {
   constructor() {
     this.loaders = {};
     this.panels = {};
-    // this.channel should get overwritten by setChannel if package versions are
-    // correct and AddonStore is a proper singleton. If not, this will be null
-    // (currently required by @storybook/react-native getStorybookUI)
     this.channel = null;
     this.preview = null;
     this.database = null;
   }
 
   getChannel() {
+    // this.channel should get overwritten by setChannel if package versions are
+    // correct and AddonStore is a proper singleton. If not, throw.
+    if (!this.channel) {
+      throw new Error(
+        'Accessing nonexistent addons channel, see https://storybook.js.org/basics/faq/#why-is-there-no-addons-channel'
+      );
+    }
     return this.channel;
   }