SvelteKit: Add experimental page and navigation mocking

code/e2e-tests/framework-svelte.spec.ts

@@ -1,24 +1,23 @@
 /* eslint-disable jest/no-disabled-tests */
 import { test, expect } from '@playwright/test';
 import process from 'process';
-import dedent from 'ts-dedent';
 import { SbPage } from './util';
 
 const storybookUrl = process.env.STORYBOOK_URL || 'http://localhost:6006';
 const templateName = process.env.STORYBOOK_TEMPLATE_NAME;
 
+test.beforeEach(async ({ page }) => {
+  await page.goto(storybookUrl);
+  await new SbPage(page).waitUntilLoaded();
+});
+
 test.describe('Svelte', () => {
   test.skip(
     // eslint-disable-next-line jest/valid-title
     !templateName?.includes('svelte'),
     'Only run this test on Svelte'
   );
 
-  test.beforeEach(async ({ page }) => {
-    await page.goto(storybookUrl);
-    await new SbPage(page).waitUntilLoaded();
-  });
-
   test('JS story has auto-generated args table', async ({ page }) => {
     const sbPage = new SbPage(page);
 
@@ -50,4 +49,46 @@ test.describe('Svelte', () => {
     const expectedSource = '<ButtonJavaScript primary/>';
     await expect(sourceCode.textContent()).resolves.toContain(expectedSource);
   });
+
+  test('Decorators runs only once', async ({ page }) => {
+    const sbPage = new SbPage(page);
+    const lines: string[] = [];
+    page.on('console', (msg) => {
+      const text = msg.text();
+      if (text === 'decorator called') {
+        lines.push(text);
+      }
+    });
+
+    await sbPage.navigateToStory('stories/renderers/svelte/decorators-runs-once', 'default');
+    expect(lines).toHaveLength(1);
+  });
+});
+
+test.describe('SvelteKit', () => {
+  test.skip(
+    // eslint-disable-next-line jest/valid-title
+    !templateName?.includes('svelte-kit'),
+    'Only run this test on SvelteKit'
+  );
+
+  test('Links are logged in Actions panel', async ({ page }) => {
+    const sbPage = new SbPage(page);
+
+    await sbPage.navigateToStory('stories/sveltekit/modules/hrefs', 'default-actions');
+    const root = sbPage.previewRoot();
+    const link = root.locator('a', { hasText: 'Link to /basic-href' });
+    await link.click();
+
+    await sbPage.viewAddonPanel('Actions');
+    const basicLogItem = await page.locator('#storybook-panel-root #panel-tab-content', {
+      hasText: `/basic-href`,
+    });
+
+    await expect(basicLogItem).toBeVisible();
+    const complexLogItem = await page.locator('#storybook-panel-root #panel-tab-content', {
+      hasText: `/deep/nested`,
+    });
+    await expect(complexLogItem).toBeVisible();
+  });
 });

code/frameworks/sveltekit/README.md

@@ -13,6 +13,8 @@ Check out our [Frameworks API](https://storybook.js.org/blog/framework-api/) ann
   - [In a project with Storybook](#in-a-project-with-storybook)
     - [Automatic migration](#automatic-migration)
     - [Manual migration](#manual-migration)
+- [How to mock](#how-to-mock)
+  - [Mocking links](#mocking-links)
 - [Troubleshooting](#troubleshooting)
   - [Error: `ERR! SyntaxError: Identifier '__esbuild_register_import_meta_url__' has already been declared` when starting Storybook](#error-err-syntaxerror-identifier-__esbuild_register_import_meta_url__-has-already-been-declared-when-starting-storybook)
   - [Error: `Cannot read properties of undefined (reading 'disable_scroll_handling')` in preview](#error-cannot-read-properties-of-undefined-reading-disable_scroll_handling-in-preview)
@@ -26,10 +28,10 @@ However SvelteKit has some [Kit-specific modules](https://kit.svelte.dev/docs/mo
 | **Module**                                                                         | **Status**             | **Note**                                                                                                                            |
 | ---------------------------------------------------------------------------------- | ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
 | [`$app/environment`](https://kit.svelte.dev/docs/modules#$app-environment)         | ✅ Supported           | `version` is always empty in Storybook.                                                                                             |
-| [`$app/forms`](https://kit.svelte.dev/docs/modules#$app-forms)                     | ⏳ Future              | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999)                                          |
-| [`$app/navigation`](https://kit.svelte.dev/docs/modules#$app-navigation)           | ⏳ Future              | Will use mocks. Tracked in [#20999](https://github.com/storybookjs/storybook/issues/20999)                                          |
+| [`$app/forms`](https://kit.svelte.dev/docs/modules#$app-forms)                     | ✅ Supported           | See [How to mock](#how-to-mock)                                                                                                     |
+| [`$app/navigation`](https://kit.svelte.dev/docs/modules#$app-navigation)           | ✅ Supported           | See [How to mock](#how-to-mock)                                                                                                     |
 | [`$app/paths`](https://kit.svelte.dev/docs/modules#$app-paths)                     | ✅ Supported           | Requires SvelteKit 1.4.0 or newer                                                                                                   |
-| [`$app/stores`](https://kit.svelte.dev/docs/modules#$app-stores)                   | ✅ Supported           | Mocks planned, so you can set different store values per story.                                                                     |
+| [`$app/stores`](https://kit.svelte.dev/docs/modules#$app-stores)                   | ✅ Supported           | See [How to mock](#how-to-mock)                                                                                                     |
 | [`$env/dynamic/private`](https://kit.svelte.dev/docs/modules#$env-dynamic-private) | ⛔ Not supported       | They are meant to only be available server-side, and Storybook renders all components on the client.                                |
 | [`$env/dynamic/public`](https://kit.svelte.dev/docs/modules#$env-dynamic-public)   | 🚧 Partially supported | Only supported in development mode. Storybook is built as a static app with no server-side API so cannot dynamically serve content. |
 | [`$env/static/private`](https://kit.svelte.dev/docs/modules#$env-static-private)   | ⛔ Not supported       | They are meant to only be available server-side, and Storybook renders all components on the client.                                |
@@ -100,6 +102,77 @@ yarn remove storybook-builder-vite
 yarn remove @storybook/builder-vite
 ```
 
+## How to mock
+
+To mock a SvelteKit import you can set it on `parameters.sveltekit_experimental`:
+
+```ts
+export const MyStory = {
+  parameters: {
+    sveltekit_experimental: {
+      stores: {
+        page: {
+          data: {
+            test: 'passed',
+          },
+        },
+        navigating: {
+          route: {
+            id: '/storybook',
+          },
+        },
+        updated: true,
+      },
+    },
+  },
+};
+```
+
+You can add the name of the module you want to mock to `parameters.sveltekit_experimental` (in the example above we are mocking the `stores` module which correspond to `$app/stores`) and then pass the following kind of objects:
+
+| Module                                            | Path in parameters                                           | Kind of objects                                                                                    |
+| ------------------------------------------------- | ------------------------------------------------------------ | -------------------------------------------------------------------------------------------------- |
+| `import { page } from "$app/stores"`              | `parameters.sveltekit_experimental.stores.page`              | A Partial of the page store                                                                        |
+| `import { navigating } from "$app/stores"`        | `parameters.sveltekit_experimental.stores.navigating`        | A Partial of the navigating store                                                                  |
+| `import { updated } from "$app/stores"`           | `parameters.sveltekit_experimental.stores.updated`           | A boolean representing the value of updated (you can also access `check()` which will be a noop)   |
+| `import { goto } from "$app/navigation"`          | `parameters.sveltekit_experimental.navigation.goto`          | A callback that will be called whenever goto is called                                             |
+| `import { invalidate } from "$app/navigation"`    | `parameters.sveltekit_experimental.navigation.invalidate`    | A callback that will be called whenever invalidate is called                                       |
+| `import { invalidateAll } from "$app/navigation"` | `parameters.sveltekit_experimental.navigation.invalidateAll` | A callback that will be called whenever invalidateAll is called                                    |
+| `import { afterNavigate } from "$app/navigation"` | `parameters.sveltekit_experimental.navigation.afterNavigate` | An object that will be passed to the afterNavigate function (which will be invoked onMount) called |
+| `import { enhance } from "$app/forms"`            | `parameters.sveltekit_experimental.forms.enhance`            | A callback that will called when a form with `use:enhance` is submitted                            |
+
+All the other functions are still exported as `noop` from the mocked modules so that your application will still work.
+
+### Mocking links
+
+The default link-handling behavior (ie. clicking an `<a />` tag with an `href` attribute) is to log an action to the Actions panel.
+
+You can override this by setting an object on `parameter.sveltekit_experimental.hrefs`, where the keys are strings representing an href and the values are objects typed as `{ callback: (href, event) => void, asRegex?: boolean }`.
+
+If you have an `<a />` tag inside your code with the `href` attribute that matches one or more of the links defined (treated as regex based on the `asRegex` property) the corresponding `callback` will be called.
+
+Example:
+
+```ts
+export const MyStory = {
+  parameters: {
+    sveltekit_experimental: {
+      hrefs: {
+        '/basic-href': (to, event) => {
+          console.log(to, event);
+        },
+        '/root.*': {
+          callback: (to, event) => {
+            console.log(to, event);
+          },
+          asRegex: true,
+        },
+      },
+    },
+  },
+};
+```
+
 ## Troubleshooting
 
 ### Error: `ERR! SyntaxError: Identifier '__esbuild_register_import_meta_url__' has already been declared` when starting Storybook
@@ -125,3 +198,4 @@ You'll experience this if anything in your story is importing from `$app/forms`
 ## Acknowledgements
 
 Integrating with SvelteKit would not have been possible if it weren't for the fantastic efforts by the Svelte core team - especially [Ben McCann](https://twitter.com/benjaminmccann) - to make integrations with the wider ecosystem possible.
+A big thank you also goes out to [Paolo Ricciuti](https://twitter.com/PaoloRicciuti) for improving the mocking capabilities.

code/frameworks/sveltekit/package.json

@@ -29,6 +29,9 @@
       "require": "./dist/index.js",
       "import": "./dist/index.mjs"
     },
+    "./dist/preview.mjs": {
+      "import": "./dist/preview.mjs"
+    },
     "./preset": {
       "types": "./dist/preset.d.ts",
       "require": "./dist/preset.js"
@@ -43,13 +46,14 @@
     "README.md",
     "*.js",
     "*.d.ts",
-    "!src/**/*"
+    "src/mocks/**/*"
   ],
   "scripts": {
     "check": "node --loader ../../../scripts/node_modules/esbuild-register/loader.js -r ../../../scripts/node_modules/esbuild-register/register.js ../../../scripts/prepare/check.ts",
     "prep": "node --loader ../../../scripts/node_modules/esbuild-register/loader.js -r ../../../scripts/node_modules/esbuild-register/register.js ../../../scripts/prepare/bundle.ts"
   },
   "dependencies": {
+    "@storybook/addon-actions": "workspace:*",
     "@storybook/builder-vite": "workspace:*",
     "@storybook/svelte": "workspace:*",
     "@storybook/svelte-vite": "workspace:*"
@@ -72,6 +76,7 @@
   "bundler": {
     "entries": [
       "./src/index.ts",
+      "./src/preview.ts",
       "./src/preset.ts"
     ],
     "platform": "node"

code/frameworks/sveltekit/src/mocks/app/forms.ts

@@ -0,0 +1,17 @@
+export function enhance(form: HTMLFormElement) {
+  const listener = (e: Event) => {
+    e.preventDefault();
+    const event = new CustomEvent('storybook:enhance');
+    window.dispatchEvent(event);
+  };
+  form.addEventListener('submit', listener);
+  return {
+    destroy() {
+      form.removeEventListener('submit', listener);
+    },
+  };
+}
+
+export function applyAction() {}
+
+export function deserialize() {}

code/frameworks/sveltekit/src/mocks/app/navigation.ts

@@ -0,0 +1,43 @@
+import { getContext, onMount, setContext } from 'svelte';
+
+export async function goto(...args: any[]) {
+  const event = new CustomEvent('storybook:goto', {
+    detail: args,
+  });
+  window.dispatchEvent(event);
+}
+
+export function setAfterNavigateArgument(afterNavigateArgs: any) {
+  setContext('after-navigate-args', afterNavigateArgs);
+}
+
+export function afterNavigate(cb: any) {
+  const argument = getContext('after-navigate-args');
+  onMount(() => {
+    if (cb && cb instanceof Function) {
+      cb(argument);
+    }
+  });
+}
+
+export function onNavigate() {}
+
+export function beforeNavigate() {}
+
+export function disableScrollHandling() {}
+
+export async function invalidate(...args: any[]) {
+  const event = new CustomEvent('storybook:invalidate', {
+    detail: args,
+  });
+  window.dispatchEvent(event);
+}
+
+export async function invalidateAll() {
+  const event = new CustomEvent('storybook:invalidateAll');
+  window.dispatchEvent(event);
+}
+
+export function preloadCode() {}
+
+export function preloadData() {}

code/frameworks/sveltekit/src/mocks/app/stores.ts

@@ -0,0 +1,32 @@
+import { getContext, setContext } from 'svelte';
+
+function createMockedStore(contextName: string) {
+  return [
+    {
+      subscribe(runner: any) {
+        const page = getContext(contextName);
+        runner(page);
+        return () => {};
+      },
+    },
+    (value: unknown) => {
+      setContext(contextName, value);
+    },
+  ] as const;
+}
+
+export const [page, setPage] = createMockedStore('page-ctx');
+export const [navigating, setNavigating] = createMockedStore('navigating-ctx');
+const [updated, setUpdated] = createMockedStore('updated-ctx');
+
+(updated as any).check = () => {};
+
+export { updated, setUpdated };
+
+export function getStores() {
+  return {
+    page,
+    navigating,
+    updated,
+  };
+}

code/frameworks/sveltekit/src/plugins/config-overrides.ts

@@ -1,4 +1,4 @@
-import type { Plugin } from 'vite';
+import { type Plugin } from 'vite';
 
 export function configOverrides() {
   return {

code/frameworks/sveltekit/src/plugins/mock-sveltekit-stores.ts

@@ -0,0 +1,17 @@
+import { resolve } from 'node:path';
+import { mergeConfig, type Plugin } from 'vite';
+
+export function mockSveltekitStores() {
+  return {
+    name: 'storybook:sveltekit-mock-stores',
+    enforce: 'post',
+    config: (config) =>
+      mergeConfig(config, {
+        resolve: {
+          alias: {
+            $app: resolve(__dirname, '../src/mocks/app/'),
+          },
+        },
+      }),
+  } satisfies Plugin;
+}

code/frameworks/sveltekit/src/preset.ts

@@ -4,6 +4,7 @@ import type { PresetProperty } from '@storybook/types';
 import { withoutVitePlugins } from '@storybook/builder-vite';
 import { dirname, join } from 'path';
 import { configOverrides } from './plugins/config-overrides';
+import { mockSveltekitStores } from './plugins/mock-sveltekit-stores';
 import { type StorybookConfig } from './types';
 
 const getAbsolutePath = <I extends string>(input: I): I =>
@@ -13,6 +14,10 @@ export const core: PresetProperty<'core', StorybookConfig> = {
   builder: getAbsolutePath('@storybook/builder-vite'),
   renderer: getAbsolutePath('@storybook/svelte'),
 };
+export const previewAnnotations: StorybookConfig['previewAnnotations'] = (entry = []) => [
+  ...entry,
+  join(dirname(require.resolve('@storybook/sveltekit/package.json')), 'dist/preview.mjs'),
+];
 
 export const viteFinal: NonNullable<StorybookConfig['viteFinal']> = async (config, options) => {
   const baseConfig = await svelteViteFinal(config, options);
@@ -25,7 +30,9 @@ export const viteFinal: NonNullable<StorybookConfig['viteFinal']> = async (confi
       'vite-plugin-sveltekit-compile',
       'vite-plugin-sveltekit-guard',
     ])
-  ).concat(configOverrides());
+  )
+    .concat(configOverrides())
+    .concat(mockSveltekitStores());
 
   return { ...baseConfig, plugins };
 };