Merge pull request #15470 from storybookjs/chore_loader_docs_updates

Chore: (Docs) Updates the loader docs

docs/snippets/angular/loader-story.mdx.mdx

@@ -0,0 +1,28 @@
+```md
+<!-- TodoItem.stories.mdx -->
+
+import { Meta, Story } from '@storybook/addon-docs/blocks';
+
+import TodoItem from './TodoItem';
+
+import fetch from 'node-fetch';
+
+<Meta title="Examples/Loader" component={TodoItem} />
+
+<Story
+  name="Primary"
+  loaders={[
+    async () => ({
+      todo: await (
+        await fetch("https://jsonplaceholder.typicode.com/todos/1")
+      ).json(),
+    }),
+  ]}
+>
+  {(args, { loaded: { todo } }) => ({
+    props: {
+      todo: todo,
+    },
+  })}
+</Story>
+```

docs/snippets/angular/loader-story.ts.mdx

@@ -0,0 +1,37 @@
+```ts
+// TodoItem.stories.ts
+
+import { moduleMetadata, Story, Meta } from '@storybook/angular';
+
+import fetch from 'node-fetch';
+
+import { CommonModule } from '@angular/common';
+
+import TodoItem from './TodoItem';
+
+export default {
+  component: TodoItem,
+  decorators: [
+    moduleMetadata({
+      declarations: [TodoItem],
+      imports: [CommonModule],
+    }),
+  ],
+  title: 'Examples/Loader',
+} as Meta;
+
+export const Primary = (args, { loaded: { todo } }) => {
+  return {
+    props: {
+      args,
+      todo,
+    },
+  };
+};
+
+Primary.loaders = [
+  async () => ({
+    todo: await (await fetch('https://jsonplaceholder.typicode.com/todos/1')).json(),
+  }),
+];
+```

docs/snippets/svelte/storybook-preview-global-loader.js.mdx → docs/snippets/common/storybook-preview-global-loader.js.mdx

@@ -5,7 +5,7 @@ import fetch from 'node-fetch';
 
 export const loaders = [
   async () => ({
-    currentUser: (await fetch('https://jsonplaceholder.typicode.com/users/1')).json(),
+    currentUser: await (await fetch('https://jsonplaceholder.typicode.com/users/1')).json(),
   }),
 ];
 ```

docs/snippets/react/loader-story.js.mdx

@@ -7,6 +7,11 @@ import fetch from 'node-fetch';
 
 import { TodoItem } from './TodoItem';
 
+export default {
+  component: TodoItem,
+  title: 'Examples/Loader',
+};
+
 export const Primary = (args, { loaded: { todo } }) => <TodoItem {...args} {...todo} />;
 Primary.loaders = [
   async () => ({

docs/snippets/react/loader-story.mdx.mdx

@@ -0,0 +1,26 @@
+```md
+<!-- TodoItem.stories.mdx -->
+
+import { Meta, Story } from '@storybook/addon-docs';
+
+import fetch from 'node-fetch';
+
+import { TodoItem } from './TodoItem';
+
+<Meta title="Examples/Loader" component={TodoItem} />
+
+<Story
+  name="Primary"
+  loaders={[
+    async () => ({
+      todo: await (
+        await fetch("https://jsonplaceholder.typicode.com/todos/1")
+      ).json(),
+    }),
+  ]}
+>
+  {(args, { loaded: { todo } }) => (
+    <TodoItem {...args} todo={todo} />
+  )}
+</Story>
+```

docs/snippets/svelte/loader-story.js.mdx

@@ -5,14 +5,19 @@ import fetch from 'node-fetch';
 
 import TodoItem from './TodoItem.svelte';
 
+export default {
+  component: TodoItem,
+  title: 'Examples/Loader',
+};
+
 export const Primary = (args, { loaded: { todo } }) => ({
   Component: TodoItem,
-  props: {...args, ...todo},
+  props: { ...args, ...todo },
 });
 
 Primary.loaders = [
   async () => ({
-    todo: (await fetch('https://jsonplaceholder.typicode.com/todos/1')).json(),
+    todo: await (await fetch('https://jsonplaceholder.typicode.com/todos/1')).json(),
   }),
 ];
 ```

docs/snippets/svelte/loader-story.mdx.mdx

@@ -0,0 +1,30 @@
+```md
+<!-- TodoItem.stories.mdx -->
+
+import { Meta, Story } from '@storybook/addon-docs';
+
+import TodoItem from './TodoItem.svelte';
+
+import fetch from 'node-fetch';
+
+<Meta title="Examples/Loader" component={TodoItem} />
+
+<Story
+  name="Primary"
+  loaders={[
+    async () => ({
+      todo: await (
+        await fetch("https://jsonplaceholder.typicode.com/todos/1")
+      ).json(),
+    }),
+  ]}
+>
+  {(args, { loaded: { todo } }) => ({
+    Component: SampleLoaderComponent,
+    props: {
+      ...args,
+      todo,
+    },
+  })}
+</Story>
+```

docs/snippets/vue/loader-story.3.js.mdx

@@ -0,0 +1,28 @@
+```js
+// TodoItem.stories.js
+
+import TodoItem from './TodoItem.vue';
+
+import fetch from 'node-fetch';
+
+export default {
+  component: TodoItem,
+  title: 'Examples/Loader',
+};
+
+export const Primary = (args, { loaded: { todo } }) => {
+  return {
+    components: { TodoItem },
+    setup() {
+      return { args, todo: todo };
+    },
+    template: `<TodoItem :todo="todo"/>`,
+  };
+};
+
+Primary.loaders = [
+  async () => ({
+    todo: await (await fetch('https://jsonplaceholder.typicode.com/todos/1')).json(),
+  }),
+];
+```

docs/snippets/vue/loader-story.mdx.mdx

@@ -0,0 +1,30 @@
+```md
+<!-- TodoItem.stories.mdx -->
+
+import { Meta, Story } from '@storybook/addon-docs';
+
+import TodoItem from './TodoItem.vue';
+
+import fetch from 'node-fetch';
+
+<Meta title="Examples/Loader" component={TodoItem} />
+
+<Story
+  name="Primary"
+  loaders={[
+    async () => ({
+      todo: await (
+        await fetch("https://jsonplaceholder.typicode.com/todos/1")
+      ).json(),
+    }),
+  ]}
+>
+  {(args, { loaded: { todo } }) => ({
+    components: { TodoItem },
+    setup() {
+      return { args, todo: todo };
+    },
+    template: `<TodoItem :todo="todo"/>`,
+  })}
+</Story>
+```

docs/writing-stories/loaders.md

@@ -2,30 +2,36 @@
 title: 'Loaders (experimental)'
 ---
 
-Loaders (experimental) are asynchronous functions that load data for a story and its [decorators](./decorators.md). A story's loaders run before the story renders, and the loaded data is passed into the story via its render context.
+Loaders (experimental) are asynchronous functions that load data for a story and its [decorators](./decorators.md). A story's loaders run before the story renders, and the loaded data injected into the story via its render context.
 
-Loaders can be used to load any asset, typically as a performance optimization. They were designed for to lazy load components and other large story imports. They can also be used to load remote API data to be used in a story. However, [Args](./args.md) is the recommended way to manage story data, and we're building up an ecosystem of tools and techniques around Args which might not be compatible with loaded data.
+Loaders can be used to load any asset, lazy load components, or fetch data from a remote API. This feature was designed as a performance optimization to handle large story imports. However, [Args](./args.md) is the recommended way to manage story data. We're building up an ecosystem of tools and techniques around Args that might not be compatible with loaded data.
 
-Loaders are an advanced feature ("escape hatch") and we only recommend using them if you have a specific need that can't be fulfilled by other means. They are experimental in Storybook 6.1 and the APIs are subject to change outside of the normal semver cycle.
+They are an advanced feature (i.e., escape hatch), and we only recommend using them if you have a specific need that other means can't fulfill. They are experimental in Storybook 6.1, and the APIs are subject to change outside of the normal semver cycle.
 
 ## Fetching API data
 
-Stories are isolated component examples that render internal data that's defined as part of the story or alongside the story as [args](./args.md).
+Stories are isolated component examples that render internal data defined as part of the story or alongside the story as [args](./args.md).
 
-Loaders are useful when you need to load story data externally, e.g. from a remote API. Consider the following example that fetches a todo item for display in a todo list:
+Loaders are helpful when you need to load story data externally (e.g., from a remote API). Consider the following example that fetches a todo item to display in a todo list:
 
 <!-- prettier-ignore-start -->
 
 <CodeSnippets
   paths={[
     'react/loader-story.js.mdx',
+    'react/loader-story.mdx.mdx',
+    'vue/loader-story.3.js.mdx',
+    'vue/loader-story.mdx.mdx',
+    'angular/loader-story.ts.mdx',
+    'angular/loader-story.mdx.mdx',
     'svelte/loader-story.js.mdx',
+    'svelte/loader-story.mdx.mdx',
   ]}
 />
 
 <!-- prettier-ignore-end -->
 
-The loaded data is combined into a `loaded` field on the story context, which is the second argument to a story function. In this example we spread the story's args in first, so they take priority over the static data provided by the loader.
+The response obtained from the remote API call is combined into a `loaded` field on the story context, which is the second argument to a story function. For example, in React, the story's args were spread first to prioritize them over the static data provided by the loader. With other frameworks (e.g., Angular), you can write your stories as you'd usually do.
 
 ## Global loaders
 
@@ -35,20 +41,19 @@ We can also set a loader for **all stories** via the `loaders` export of your [`
 
 <CodeSnippets
   paths={[
-    'react/storybook-preview-global-loader.js.mdx',
-    'svelte/storybook-preview-global-loader.js.mdx',
+    'common/storybook-preview-global-loader.js.mdx',
   ]}
 />
 
 <!-- prettier-ignore-end -->
 
-In this example, we load a "current user" that is available as `loaded.currentUser` for all stories.
+In this example, we load a "current user" available as `loaded.currentUser` for all stories.
 
 ## Loader inheritance
 
-Like parameters, loaders can be defined globally, at the component level and for a single story (as we’ve seen).
+Like [parameters](./parameters.md), loaders can be defined globally, at the component level, and for a single story (as we’ve seen).
 
-All loaders, defined at all levels that apply to a story, run before the story is rendered.
+All loaders, defined at all levels that apply to a story, run before the story renders in Storybook's canvas.
 
 - All loaders run in parallel
 - All results are the `loaded` field in the story context
@@ -63,3 +68,5 @@ Loaders have the following known limitations:
 
 - They are not yet compatible with the storyshots addon ([#12703](https://github.com/storybookjs/storybook/issues/12703)).
 - They are not yet compatible with inline-rendered stories in Storybook Docs ([#12726](https://github.com/storybookjs/storybook/issues/12726)).
+
+If you're interested in contributing to this feature, read our [contribution guide](../contribute/how-to-contribute.md) and submit a pull request with your work.