UI: Wait 100ms before showing spinner and fix story overlaying it

examples/official-storybook/stories/core/loaders.stories.js

@@ -9,3 +9,17 @@ export const Story = (args, { loaded }) => (
   <div>Loaded Value is {JSON.stringify(loaded, null, 2)}</div>
 );
 Story.loaders = [async () => ({ storyValue: 3 })];
+
+export const ZIndex = (args, { loaded }) => (
+  <div
+    style={{
+      position: 'relative',
+      zIndex: 1000,
+      width: '100px',
+      height: '100px',
+      background: 'coral',
+    }}
+  >
+    This story has a very high <code>z-index</code>
+  </div>
+);

examples/official-storybook/stories/core/rendering.stories.js

@@ -53,3 +53,8 @@ ArgsChange.decorators = [
     return <StoryFn />;
   },
 ];
+
+// Ensure that this story gets focus when browsed to
+//   see https://github.com/storybookjs/storybook/issues/16847
+// eslint-disable-next-line jsx-a11y/no-autofocus
+export const AutoFocus = () => <input autoFocus />;

lib/core-common/templates/base-preview-head.html

@@ -1,6 +1,17 @@
 <base target="_parent" />
 
 <style>
+  /* While we aren't showing the main block yet, but still preparing, we want everything the user
+     has rendered, which may or may not be in #root, to be display none */
+  .sb-show-preparing-story:not(.sb-show-main) > :not(.sb-preparing-story) {
+    display: none;
+  }
+
+  .sb-show-preparing-docs:not(.sb-show-main) > :not(.sb-preparing-docs) {
+    display: none;
+  }
+
+  /* Hide our own blocks when we aren't supposed to be showing them */
   :not(.sb-show-preparing-story) > .sb-preparing-story,
   :not(.sb-show-preparing-docs) > .sb-preparing-docs,
   :not(.sb-show-nopreview) > .sb-nopreview,
@@ -140,6 +151,9 @@
   .sb-preparing-story,
   .sb-preparing-docs {
     background-color: white;
+    /* Maximum possible z-index. It would be better to use stacking contexts to ensure it's always
+    on top, but this isn't possible as it would require making CSS changes that could affect user code */
+    z-index: 2147483647;
   }
 
   .sb-loader {

lib/preview-web/src/PreviewWeb.tsx

@@ -429,7 +429,7 @@ export class PreviewWeb<TFramework extends AnyFramework> {
 
     // Show a spinner while we load the next story
     if (selection.viewMode === 'story') {
-      this.view.showPreparingStory();
+      this.view.showPreparingStory({ immediate: viewModeChanged });
     } else {
       this.view.showPreparingDocs();
     }
@@ -454,7 +454,11 @@ export class PreviewWeb<TFramework extends AnyFramework> {
     >(
       this.channel,
       this.storyStore,
-      this.renderToDOM,
+      (...args) => {
+        // At the start of renderToDOM we make the story visible (see note in WebView)
+        this.view.showStoryDuringRender();
+        return this.renderToDOM(...args);
+      },
       this.mainStoryCallbacks(storyId),
       storyId,
       'story'

lib/preview-web/src/WebView.ts

@@ -8,6 +8,8 @@ import { Story } from '@storybook/store';
 
 const { document } = global;
 
+const PREPARING_DELAY = 100;
+
 const layoutClassMap = {
   centered: 'sb-main-centered',
   fullscreen: 'sb-main-fullscreen',
@@ -39,6 +41,8 @@ export class WebView {
 
   testing = false;
 
+  preparingTimeout: ReturnType<typeof setTimeout> = null;
+
   constructor() {
     // Special code for testing situations
     const { __SPECIAL_TEST_PARAMETER__ } = qs.parse(document.location.search, {
@@ -111,6 +115,7 @@ export class WebView {
   }
 
   showMode(mode: Mode) {
+    clearTimeout(this.preparingTimeout);
     Object.keys(Mode).forEach((otherMode) => {
       if (otherMode === mode) {
         document.body.classList.add(classes[otherMode]);
@@ -145,12 +150,22 @@ export class WebView {
     this.docsRoot()?.setAttribute('hidden', 'true');
   }
 
-  showPreparingStory() {
-    this.showMode(Mode.PREPARING_STORY);
+  showPreparingStory({ immediate = false } = {}) {
+    clearTimeout(this.preparingTimeout);
+
+    if (immediate) {
+      this.showMode(Mode.PREPARING_STORY);
+    } else {
+      this.preparingTimeout = setTimeout(
+        () => this.showMode(Mode.PREPARING_STORY),
+        PREPARING_DELAY
+      );
+    }
   }
 
   showPreparingDocs() {
-    this.showMode(Mode.PREPARING_DOCS);
+    clearTimeout(this.preparingTimeout);
+    this.preparingTimeout = setTimeout(() => this.showMode(Mode.PREPARING_DOCS), PREPARING_DELAY);
   }
 
   showMain() {
@@ -166,4 +181,13 @@ export class WebView {
     this.docsRoot().setAttribute('hidden', 'true');
     this.storyRoot().removeAttribute('hidden');
   }
+
+  showStoryDuringRender() {
+    // When 'showStory' is called (at the start of rendering) we get rid of our display:none
+    // from all children of the root (but keep the preparing spinner visible). This may mean
+    // that very weird and high z-index stories are briefly visible.
+    // See https://github.com/storybookjs/storybook/issues/16847 and
+    //   http://localhost:9011/?path=/story/core-rendering--auto-focus (official SB)
+    document.body.classList.add(classes.MAIN);
+  }
 }