260223:1415 20260223 nextJS & nestJS Best pratices

.agents/skills/next-best-practices/image.md

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+# Image Optimization
+
+Use `next/image` for automatic image optimization.
+
+## Always Use next/image
+
+```tsx
+// Bad: Avoid native img
+<img src="/hero.png" alt="Hero" />
+
+// Good: Use next/image
+import Image from 'next/image'
+<Image src="/hero.png" alt="Hero" width={800} height={400} />
+```
+
+## Required Props
+
+Images need explicit dimensions to prevent layout shift:
+
+```tsx
+// Local images - dimensions inferred automatically
+import heroImage from './hero.png'
+<Image src={heroImage} alt="Hero" />
+
+// Remote images - must specify width/height
+<Image src="https://example.com/image.jpg" alt="Hero" width={800} height={400} />
+
+// Or use fill for parent-relative sizing
+<div style={{ position: 'relative', width: '100%', height: 400 }}>
+  <Image src="/hero.png" alt="Hero" fill style={{ objectFit: 'cover' }} />
+</div>
+```
+
+## Remote Images Configuration
+
+Remote domains must be configured in `next.config.js`:
+
+```js
+// next.config.js
+module.exports = {
+  images: {
+    remotePatterns: [
+      {
+        protocol: 'https',
+        hostname: 'example.com',
+        pathname: '/images/**',
+      },
+      {
+        protocol: 'https',
+        hostname: '*.cdn.com', // Wildcard subdomain
+      },
+    ],
+  },
+}
+```
+
+## Responsive Images
+
+Use `sizes` to tell the browser which size to download:
+
+```tsx
+// Full-width hero
+<Image
+  src="/hero.png"
+  alt="Hero"
+  fill
+  sizes="100vw"
+/>
+
+// Responsive grid (3 columns on desktop, 1 on mobile)
+<Image
+  src="/card.png"
+  alt="Card"
+  fill
+  sizes="(max-width: 768px) 100vw, 33vw"
+/>
+
+// Fixed sidebar image
+<Image
+  src="/avatar.png"
+  alt="Avatar"
+  width={200}
+  height={200}
+  sizes="200px"
+/>
+```
+
+## Blur Placeholder
+
+Prevent layout shift with placeholders:
+
+```tsx
+// Local images - automatic blur hash
+import heroImage from './hero.png'
+<Image src={heroImage} alt="Hero" placeholder="blur" />
+
+// Remote images - provide blurDataURL
+<Image
+  src="https://example.com/image.jpg"
+  alt="Hero"
+  width={800}
+  height={400}
+  placeholder="blur"
+  blurDataURL="data:image/jpeg;base64,/9j/4AAQSkZJRg..."
+/>
+
+// Or use color placeholder
+<Image
+  src="https://example.com/image.jpg"
+  alt="Hero"
+  width={800}
+  height={400}
+  placeholder="empty"
+  style={{ backgroundColor: '#e0e0e0' }}
+/>
+```
+
+## Priority Loading
+
+Use `priority` for above-the-fold images (LCP):
+
+```tsx
+// Hero image - loads immediately
+<Image src="/hero.png" alt="Hero" fill priority />
+
+// Below-fold images - lazy loaded by default (no priority needed)
+<Image src="/card.png" alt="Card" width={400} height={300} />
+```
+
+## Common Mistakes
+
+```tsx
+// Bad: Missing sizes with fill - downloads largest image
+<Image src="/hero.png" alt="Hero" fill />
+
+// Good: Add sizes for proper responsive behavior
+<Image src="/hero.png" alt="Hero" fill sizes="100vw" />
+
+// Bad: Using width/height for aspect ratio only
+<Image src="/hero.png" alt="Hero" width={16} height={9} />
+
+// Good: Use actual display dimensions or fill with sizes
+<Image src="/hero.png" alt="Hero" fill sizes="100vw" style={{ objectFit: 'cover' }} />
+
+// Bad: Remote image without config
+<Image src="https://untrusted.com/image.jpg" alt="Image" width={400} height={300} />
+// Error: Invalid src prop, hostname not configured
+
+// Good: Add hostname to next.config.js remotePatterns
+```
+
+## Static Export
+
+When using `output: 'export'`, use `unoptimized` or custom loader:
+
+```tsx
+// Option 1: Disable optimization
+<Image src="/hero.png" alt="Hero" width={800} height={400} unoptimized />
+
+// Option 2: Global config
+// next.config.js
+module.exports = {
+  output: 'export',
+  images: { unoptimized: true },
+}
+
+// Option 3: Custom loader (Cloudinary, Imgix, etc.)
+const cloudinaryLoader = ({ src, width, quality }) => {
+  return `https://res.cloudinary.com/demo/image/upload/w_${width},q_${quality || 75}/${src}`
+}
+
+<Image loader={cloudinaryLoader} src="sample.jpg" alt="Sample" width={800} height={400} />
+```