Merge pull request #262 from reuters-graphics/mf-visible

Updates Visible

src/components/Visible/Visible.mdx

@@ -0,0 +1,31 @@
+import { Meta, Canvas } from '@storybook/blocks';
+
+import * as VisibleStories from './Visible.stories.svelte';
+
+<Meta of={VisibleStories} />
+
+# Visible
+
+The `Visible` component wraps around other components or HTML elements and uses the [Intersection Observer API](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API) to determine if they are visible on the page.
+
+This is useful for lazy loading elements, especially expensive media files or components that fetch lots of data. You can also use it trigger animations or play media once a reader scrolls a component into view.
+
+By default, `visible` will switch between `false` and `true` whenever the element is in our out of view. To trigger this just once, set the prop `once` to `true`. This is useful for loading expensive media when they first come into view and then keeping them around once they're loaded.
+
+> **Note:** Don't use this for content that's "above the fold" at the top of the page. That'll just slow down the first load of important visible content.
+
+```svelte
+<script>
+  import { Visible } from '@reuters-graphics/graphics-components';
+</script>
+
+<Visible let:visible>
+  {#if visible}
+    <p>Visible!</p>
+  {:else}
+    <p>Not yet visible.</p>
+  {/if}
+</Visible>
+```
+
+<Canvas of={VisibleStories.Demo} />

src/components/Visible/Visible.stories.svelte

@@ -1,36 +1,22 @@
 <script module lang="ts">
-  // @ts-ignore raw
-  import componentDocs from './stories/docs/component.md?raw';
-  // @ts-ignore raw
-  import defaultSnippet from './stories/snippets/default.svelte?raw';
+  import { defineMeta } from '@storybook/addon-svelte-csf';
 
   import Visible from './Visible.svelte';
 
-  import { withSource, withComponentDocs } from '$lib/docs/utils/withParams.js';
-
-  export const meta = {
+  const { Story } = defineMeta({
     title: 'Components/Utilities/Visible',
     component: Visible,
-    ...withComponentDocs(componentDocs),
-  };
+  });
 </script>
 
-<script>
-  import { Template, Story } from '@storybook/addon-svelte-csf';
-</script>
-
-<Template>
-  {#snippet children({ args })}
-    <Visible {...args}>
-      {#snippet children({ visible })}
-        {#if visible}
-          <p>Visible!</p>
-        {:else}
-          <p>Not yet visible.</p>
-        {/if}
-      {/snippet}
-    </Visible>
-  {/snippet}
-</Template>
-
-<Story name="Default" {...withSource({ svelte: defaultSnippet })} />
+<Story name="Demo" tags={['!autodocs', '!dev']}>
+  <Visible>
+    {#snippet children(visible)}
+      {#if visible}
+        <p>Visible!</p>
+      {:else}
+        <p>Not yet visible.</p>
+      {/if}
+    {/snippet}
+  </Visible>
+</Story>

src/components/Visible/Visible.svelte

@@ -1,6 +1,6 @@
 <!-- @component `Visible` [Read the docs.](https://reuters-graphics.github.io/graphics-components/?path=/docs/components-utilities-visible--docs) -->
 <script lang="ts">
-  import { onMount } from 'svelte';
+  import { onMount, type Snippet } from 'svelte';
 
   interface Props {
     /**
@@ -19,7 +19,7 @@
     right?: number;
     /** Set the Intersection Observer [threshold](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#threshold). */
     threshold?: number;
-    children?: import('svelte').Snippet<[any]>;
+    children?: Snippet<[boolean]>;
   }
 
   let {
@@ -33,15 +33,16 @@
   }: Props = $props();
 
   let visible = $state(false);
-  let container: HTMLElement = $state();
+  let container: HTMLElement | undefined = $state(undefined);
 
   onMount(() => {
     if (typeof IntersectionObserver !== 'undefined') {
       const rootMargin = `${bottom}px ${left}px ${top}px ${right}px`;
+
       const observer = new IntersectionObserver(
         (entries) => {
           visible = entries[0].isIntersecting;
-          if (visible && once) {
+          if (visible && once && container) {
             observer.unobserve(container);
           }
         },
@@ -50,16 +51,20 @@
           threshold,
         }
       );
-      observer.observe(container);
-      return () => observer.unobserve(container);
+      if (container) observer.observe(container);
+      return () => {
+        if (container) observer.observe(container);
+      };
     }
     function handler() {
-      const bcr = container.getBoundingClientRect();
-      visible =
-        bcr.bottom + bottom > 0 &&
-        bcr.right + right > 0 &&
-        bcr.top - top < window.innerHeight &&
-        bcr.left - left < window.innerWidth;
+      if (container) {
+        const bcr = container.getBoundingClientRect();
+        visible =
+          bcr.bottom + bottom > 0 &&
+          bcr.right + right > 0 &&
+          bcr.top - top < window.innerHeight &&
+          bcr.left - left < window.innerWidth;
+      }
       if (visible && once) {
         window.removeEventListener('scroll', handler);
       }
@@ -70,6 +75,7 @@
 </script>
 
 <div bind:this={container}>
-  <!-- An element or component -->
-  {@render children?.({ visible })}
+  {#if children}
+    {@render children(visible)}
+  {/if}
 </div>

src/components/Visible/stories/docs/component.md

@@ -1,19 +0,0 @@
-Wrap components or other HTML elements to determine if they are visible on the page using the [Intersection Observer API](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API).
-
-This is really useful for lazy loading elements, especially expensive media files or components that fetch lots of data. You can also use it trigger animations or play media once a reader scrolls a component into view.
-
-> **Pro tip:** Don't use this for content that's "above the fold" at the top of the page. That'll just slow down the first load of important visible content.
-
-```svelte
-<script>
-  import { Visible } from '@reuters-graphics/graphics-components';
-</script>
-
-<Visible let:visible>
-  {#if visible}
-    <p>Visible!</p>
-  {:else}
-    <p>Not yet visible.</p>
-  {/if}
-</Visible>
-```