OPHJOD-1320: Add PreloadImage component

lib/components/LazyImage/PreloadImage.stories.tsx

@@ -0,0 +1,26 @@
+import type { Meta, StoryObj } from '@storybook/react';
+import { PreloadImage } from './PreloadImage';
+
+const meta = {
+  title: 'PreloadImage',
+  component: PreloadImage,
+  tags: ['autodocs'],
+} satisfies Meta<typeof PreloadImage>;
+
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const Default: Story = {
+  parameters: {
+    docs: {
+      description: {
+        story: 'This is a lazy loading image component that preloads the image before displaying it.',
+      },
+    },
+  },
+  args: {
+    src: 'https://images.unsplash.com/photo-1523464862212-d6631d073194?q=80&w=260',
+    alt: 'Woman standing in front of a colourful wall',
+  },
+};

lib/components/LazyImage/PreloadImage.test.tsx

@@ -0,0 +1,23 @@
+import { render, screen } from '@testing-library/react';
+import { describe, expect, it } from 'vitest';
+import { PreloadImage } from './PreloadImage';
+
+describe('PreloadImage', () => {
+  it('renders without crashing', () => {
+    render(<PreloadImage src="test.jpg" alt="test image" />);
+    const imgElement = screen.getByAltText('test image');
+    expect(imgElement).toBeInTheDocument();
+  });
+
+  it('sets the alt attribute correctly', () => {
+    render(<PreloadImage src="test.jpg" alt="test image" />);
+    const imgElement = screen.getByAltText('test image');
+    expect(imgElement).toHaveAttribute('alt', 'test image');
+  });
+
+  it('applies the correct styles when the image is not loaded', () => {
+    render(<PreloadImage src="test.jpg" alt="test image" />);
+    const imgElement = screen.getByAltText('test image');
+    expect(imgElement).toHaveStyle('opacity: 0');
+  });
+});

lib/components/LazyImage/PreloadImage.tsx

@@ -0,0 +1,39 @@
+import React from 'react';
+
+interface PreloadImageProps extends React.ImgHTMLAttributes<HTMLImageElement> {
+  /** The source of the image to be preloaded */
+  src: string;
+  /** The alt text for the image */
+  alt: string;
+}
+
+/**
+ * PreloadImage is a lazy loading image component that preloads the image before displaying it.
+ */
+export const PreloadImage: React.FC<PreloadImageProps> = ({ src, alt, ...props }) => {
+  const [loaded, setLoaded] = React.useState(false);
+  const [isCached, setIsCached] = React.useState(false);
+
+  React.useEffect(() => {
+    const img = new Image();
+    img.src = src;
+    if (img.complete) {
+      setIsCached(true);
+      setLoaded(true);
+    } else {
+      img.onload = () => setLoaded(true);
+    }
+    img.onload = () => setLoaded(true);
+  }, [src]);
+
+  return (
+    <div className={`ds:flex ds:bg-secondary-5 ${props.className}`.trim()}>
+      <img
+        src={loaded ? src : undefined}
+        alt={alt}
+        style={{ opacity: loaded ? 1 : 0, transition: isCached ? 'none' : 'opacity 0.3s' }}
+        className="ds:w-full ds:h-full ds:object-cover"
+      />
+    </div>
+  );
+};

lib/components/MediaCard/MediaCard.tsx

@@ -1,6 +1,7 @@
 import React from 'react';
 import { MdFavorite, MdFavoriteBorder } from 'react-icons/md';
 import { useMediaQueries } from '../../hooks/useMediaQueries';
+import { PreloadImage } from '../LazyImage/PreloadImage';
 
 type LinkComponent =
   | {
@@ -134,7 +135,7 @@ const MediaCardVertical = ({
   to,
   children,
 }: MediaCardImplProps) => {
-  const variantImageClassNames = 'ds:object-cover ds:h-[147px]';
+  const variantImageClassNames = 'ds:object-cover ds:h-[147px] ds:min-h-[147px]';
   const labelRef = React.useRef<HTMLDivElement>(null);
   const SINGLE_LINE_LABEL_HEIGHT = 27;
   const [lineClampClassNames, setLineClampClassNames] = React.useState('ds:line-clamp-3');
@@ -151,7 +152,7 @@ const MediaCardVertical = ({
   return (
     <LinkOrDiv to={to} linkComponent={Link} className="ds:relative ds:flex ds:flex-col ds:w-[261px] ds:min-h-[299px]">
       {imageSrc ? (
-        <img className={`${variantImageClassNames}`} src={imageSrc} alt={imageAlt} />
+        <PreloadImage className={`${variantImageClassNames}`} src={imageSrc} alt={imageAlt} />
       ) : (
         <span className={`ds:w-full ds:h-full ds:bg-secondary-5 ds:max-w-[265px] ${variantImageClassNames}`}></span>
       )}
@@ -184,7 +185,7 @@ const MediaCardHorizontal = ({
       <div className="ds:shrink-0">
         {imageSrc ? (
           sm && (
-            <img
+            <PreloadImage
               className="ds:sm:w-[193px] ds:lg:w-[255px] ds:sm:min-w-full ds:sm:min-h-full ds:sm:h-0 ds:object-cover"
               src={imageSrc}
               alt={imageAlt}

lib/components/MediaCard/__snapshots__/MediaCard.test.tsx.snap

@@ -4,11 +4,15 @@ exports[`MediaCard > renders the MediaCard component with default vertical varia
 <div
   class="ds:overflow-clip ds:rounded ds:shadow-border ds:bg-white ds:relative ds:flex ds:flex-col ds:w-[261px] ds:min-h-[299px]"
 >
-  <img
-    alt="Image for default"
-    class="ds:object-cover ds:h-[147px]"
-    src="default.jpg"
-  />
+  <div
+    class="ds:flex ds:bg-secondary-5 ds:object-cover ds:h-[147px] ds:min-h-[147px]"
+  >
+    <img
+      alt="Image for default"
+      class="ds:w-full ds:h-full ds:object-cover"
+      style="opacity: 0; transition: opacity 0.3s;"
+    />
+  </div>
   <div
     class="ds:px-5 ds:pt-4 ds:pb-5 ds:text-black ds:flex ds:flex-col ds:justify-between ds:h-full ds:flex-nowrap"
   >