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Performance

Harold 1.3.0 introduces comprehensive performance optimizations to help your sites achieve excellent Core Web Vitals scores and faster load times.

Automatic Optimizations (Enabled by Default)

CSS Minification

All CSS output is automatically minified using cssnano, reducing file sizes by 30-50%.

What it does:

  • Removes whitespace and comments
  • Optimizes colors, units, and other values
  • Merges duplicate selectors
  • Removes redundant code

Configuration:

{
  "minifyCss": true
}

Disable it if needed (not recommended):

{
  "minifyCss": false
}

HTML Minification

All HTML output is automatically minified, reducing file sizes by 20-40%.

What it does:

  • Removes whitespace and comments
  • Minifies inline CSS and JavaScript
  • Removes redundant attributes
  • Uses short doctype

Configuration:

{
  "minifyHtml": true
}

Disable it if needed (not recommended):

{
  "minifyHtml": false
}

Web Vitals Improvements

Automatic Image Optimization

Images in markdown posts automatically get optimized for better Core Web Vitals scores.

Automatic Features:

  1. Width & Height Attributes - Prevents Cumulative Layout Shift (CLS)
  2. Lazy Loading - Native browser loading="lazy" for better performance
  3. Async Decoding - Non-blocking rendering with decoding="async"

Example:

Input markdown:

![My image](assets/images/photo.jpg)

Output HTML:

<img src="assets/images/photo.jpg" 
     alt="My image" 
     width="800" 
     height="600" 
     loading="lazy" 
     decoding="async" />

Note: Remote images (URLs) won't get automatic dimensions. Specify them manually:

<img src="https://example.com/image.jpg" 
     alt="Remote image" 
     width="800" 
     height="600" />

responsiveImg Helper

For advanced image handling, use the responsiveImg Handlebars helper:

Basic usage:

{{responsiveImg 
  src="assets/images/photo.jpg" 
  alt="My photo"
}}

With explicit dimensions:

{{responsiveImg 
  src="assets/images/hero.jpg" 
  alt="Hero image"
  width="1200"
  height="600"
}}

Hero image (load immediately):

{{responsiveImg 
  src="assets/images/hero.jpg" 
  alt="Hero image"
  loading="eager"
  className="hero"
}}

Responsive image with multiple sizes:

{{responsiveImg 
  src="assets/images/gallery.jpg" 
  alt="Gallery"
  srcset="assets/images/gallery-small.jpg 480w, assets/images/gallery-medium.jpg 800w, assets/images/gallery-large.jpg 1200w"
  sizes="(max-width: 600px) 480px, (max-width: 1000px) 800px, 1200px"
}}

Parameters:

  • src (required) - Image source path
  • alt - Alt text for accessibility (recommended)
  • width - Image width (auto-detected if not provided)
  • height - Image height (auto-detected if not provided)
  • loading - "lazy" (default) or "eager" for above-the-fold images
  • decoding - "async" (default) or "sync"
  • className - CSS class name
  • srcset - Responsive image sources for different screen sizes
  • sizes - Media query sizes for responsive images

When to use eager loading:

  • Hero/banner images above the fold
  • Logo images
  • Critical UI elements
  • Images needed for initial render

When to use lazy loading (default):

  • Gallery images
  • Blog post content images
  • Footer images
  • Any below-the-fold content

Responsive images example:

Create multiple image sizes:

# Original
assets/images/photo.jpg (1200x800)

# Smaller versions
assets/images/photo-small.jpg (480x320)
assets/images/photo-medium.jpg (800x533)

Use with srcset:

{{responsiveImg 
  src="assets/images/photo.jpg" 
  alt="Responsive photo"
  srcset="assets/images/photo-small.jpg 480w, assets/images/photo-medium.jpg 800w, assets/images/photo.jpg 1200w"
  sizes="(max-width: 600px) 100vw, (max-width: 1000px) 80vw, 1200px"
}}

The browser will automatically choose the best image based on screen size and resolution!

PostsList Images

The postsList helper now includes optimized images:

{{postsList
  perPageLimit=6
  noImage=false
}}

All cover images automatically include:

  • loading="lazy"
  • decoding="async"
  • Proper alt text from post title

Performance Best Practices

1. Optimize Images Before Adding

  • Compress images using tools like TinyPNG or ImageOptim
  • Use modern formats (WebP) when possible
  • Create multiple sizes for responsive images

2. Use Lazy Loading Strategically

  • Lazy loading (default) for below-the-fold images
  • Eager loading for above-the-fold images (hero, logo)
<!-- Above the fold - load immediately -->
{{responsiveImg 
  src="assets/images/hero.jpg" 
  alt="Hero"
  loading="eager"
}}

<!-- Below the fold - lazy load -->
{{responsiveImg 
  src="assets/images/gallery.jpg" 
  alt="Gallery"
  loading="lazy"
}}

3. Specify Image Dimensions

Always include width and height for images to prevent layout shift:

<!-- Local images - dimensions detected automatically -->
![Alt text](assets/images/photo.jpg)

<!-- Remote images - specify manually -->
<img src="https://example.com/image.jpg" 
     alt="Remote" 
     width="800" 
     height="600" />

4. Monitor Performance

Use these tools to check your site's performance:

Configuration Example

Complete .haroldrc with performance options:

{
  "mdFilesDirName": "posts",
  "mdFilesLayoutsDirName": "blog-layouts",
  "outputDirName": "build",
  "minifyCss": true,
  "minifyHtml": true
}

Troubleshooting

Images Missing Dimensions

Issue: Some images don't have width/height attributes

Solutions:

  1. Ensure images exist in the filesystem before build
  2. For remote images, add dimensions manually
  3. Check build output for yellow warnings about missing dimensions

Minification Disabled

Issue: HTML/CSS files are not minified

Solutions:

  1. Check .haroldrc for minifyHtml and minifyCss settings
  2. Run npm install to ensure all dependencies are installed
  3. Clear build directory and rebuild

Layout Shift Still Occurring

Solutions:

  1. Check all images have explicit dimensions
  2. Reserve space for ads/embeds with min-height
  3. Use CSS aspect-ratio for responsive containers

Migration from Older Versions

All optimizations are backward compatible and enabled by default. No code changes required!

To update your project:

  1. Update harold-scripts in your package.json
  2. Run npm install
  3. Rebuild your site

Your site will automatically benefit from:

  • ✅ Minified HTML and CSS
  • ✅ Optimized images with dimensions
  • ✅ Lazy loading
  • ✅ Better Web Vitals scores

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