Mastering EDS Block Debugging - A Developer's Guide to Edge Delivery Services

Debugging Adobe Edge Delivery Services blocks can feel like solving a puzzle in the dark, but with the right tools and techniques, you can master EDS debugging and build robust, performant blocks.

Why EDS Debugging Feels Different

Debugging Adobe Edge Delivery Services (EDS) blocks presents unique challenges. Unlike traditional web development, EDS runs content through a sophisticated pipeline: Document Creation → Markdown Conversion → HTML Generation → Block Processing → Final Rendering.

This transformation process creates multiple potential failure points. Traditional debugging approaches often fall short because EDS loads blocks using constructed import paths that can't be easily modified. Content exists in both "served" and "rendered" states with different structures. Timing conflicts arise between EDS processing and custom component logic. Modern web components can clash with EDS's styling system.

Consider this common scenario - you've built a web component that works perfectly in isolation, but when integrated with EDS, users see a blank screen. The browser console shows no errors, the component loads successfully, yet nothing appears. This exact issue has stumped developers for hours. The root cause is often a Shadow DOM versus EDS processing race condition where the component clears the DOM before preserving EDS's critical data-block-status attributes.

Starting with Basic EDS Blocks

Let's begin with a simple EDS block to understand the foundation:

// blocks/hero/hero.js - A simple EDS block

export default function decorate(block) {
  const heading = block.querySelector('h1');
  const text = block.querySelector('p');
  if (heading) {
    heading.classList.add('hero-title');
  }

  if (text) {
    text.classList.add('hero-text');
  }
}

This basic block works, but when issues arise, you have limited visibility into what's happening. Common problems include blocks not loading at all, styling not applying correctly, performance issues with complex blocks, and race conditions with EDS processing.

Adding Debug Capabilities Step by Step

Let's enhance our basic block with debugging capabilities, building up systematically.

Step 1 - Add Basic Logging

// blocks/hero/hero.js - With basic debugging

export default function decorate(block) {
  console.log('[HERO] Starting decoration');
  const heading = block.querySelector('h1');
  const text = block.querySelector('p');
  console.log('[HERO] Found elements:', { heading: !!heading, text: !!text });

  if (heading) {
    heading.classList.add('hero-title');
    console.log('[HERO] Added hero-title class');
  }

  if (text) {
    text.classList.add('hero-text');
    console.log('[HERO] Added hero-text class');
  }
  console.log('[HERO] Decoration complete');
}

Step 2 - Add Error Handling

// blocks/hero/hero.js - With error handling

export default function decorate(block) {
  try {
    console.log('[HERO] Starting decoration');
    const heading = block.querySelector('h1');
    const text = block.querySelector('p');
    if (heading) {
      heading.classList.add('hero-title');
    }
    if (text) {
      text.classList.add('hero-text');
    }
    console.log('[HERO] Decoration complete');

  } catch (error) {

    console.error('[HERO] Decoration failed:', error);
  
    // Provide fallback content
    block.innerHTML = '<p>Hero content temporarily unavailable</p>';
  }
}

Step 3 - Add Performance Monitoring

// blocks/hero/hero.js - With performance monitoring

export default function decorate(block) {
  const startTime = performance.now();
  
  try {
    console.log('[HERO] Starting decoration');
    const heading = block.querySelector('h1');
    const text = block.querySelector('p');
    if (heading) {
      heading.classList.add('hero-title');
    }

    if (text) {
      text.classList.add('hero-text');
    }
    const endTime = performance.now();
    console.log(`[HERO] Decoration complete in ${(endTime - startTime).toFixed(2)}ms`);
  } catch (error) {
    console.error('[HERO] Decoration failed:', error);
    block.innerHTML = '<p>Hero content temporarily unavailable</p>';
  }
}

Understanding EDS's Dynamic Loading System

EDS loads blocks using a specific pattern that affects debugging:

// In scripts/aem.js - How EDS loads blocks

const mod = await import(`/blocks/${blockName}/${blockName}.js`);
if (mod.default) {
  await mod.default(block);
}

This means EDS always calls blocks by their exact filename. You can't simply change the import path to load a different version for testing.

The File Replacement Strategy

To test enhanced or instrumented versions of blocks, you need to use file replacement:

# 1. Backup the original
cp blocks/hero/hero.js blocks/hero/hero-backup.js
# 2. Replace with enhanced version
cp blocks/hero/hero-enhanced.js blocks/hero/hero.js
# 3. Test your changes
# EDS will automatically load the enhanced version
# 4. Restore the original
cp blocks/hero/hero-backup.js blocks/hero/hero.js
# Or use git to restore
git restore blocks/hero/hero.js

Advanced Debugging with Instrumentation

For complex performance issues and deep debugging, you can create comprehensive instrumentation. This transforms your basic blocks into powerful debugging tools.

Instrumentation wraps your existing functions with monitoring code that captures function execution times, memory usage patterns, DOM mutations and changes, async operation tracking, error patterns and recovery, and complete execution flow.

Instead of manually adding debugging to every function, instrumentation automatically wraps them:

// Original basic block

export default function decorate(block) {
  const heading = block.querySelector('h1');
  if (heading) {
    heading.classList.add('hero-title');
  }
}

// Becomes instrumented version (automatically generated)
export default function decorate(block) {
  return window.instrumentFunction('decorate', arguments, () => {
    const heading = block.querySelector('h1');
    if (heading) {
      heading.classList.add('hero-title');
    }
  });
}

Requesting AI-Assisted Instrumentation

The most effective way to create comprehensive instrumentation is to use AI assistance. Here's the prompt that works with any AI assistant:

<hr/>

Please create comprehensive instrumentation for this EDS project's JavaScript files. I need detailed performance metrics, function call traces, execution timing data, variable scope analysis, memory usage patterns, and program flow information during execution.

Requirements: Create a reusable instrumentation.js file that can wrap any function with performance monitoring. Create instrumented versions of all major JavaScript files. Capture function execution times, memory usage, DOM mutations, async operations. Generate telemetry data in a structured format suitable for analysis. Ensure instrumentation has minimal impact on execution performance.

<hr/>

After creating instrumented versions, you can access detailed performance data:

// In browser console after loading instrumented version

window.getInstrumentationReport()

// Example output:
{
  "totalFunctionCalls": 127,
  "totalExecutionTime": 89.4,
  "functionMetrics": {
    "decorate": {
      "calls": 3,
      "totalTime": 15.2,
      "averageTime": 5.07,
      "memoryIncrease": 1024
    }
  },
  "domMutations": 47,
  "asyncOperations": 8,
  "memoryUsage": {
    "initial": "2.85MB",
    "final": "3.46MB",
    "peak": "3.92MB"
  }
}

Browser Console Debug Tools

Set up comprehensive debugging tools in your browser console:

// Add to your test files for instant debugging access

window.debugEDS = {
  // Get all blocks on the page
  getBlocks: () => document.querySelectorAll('[data-block-name]'),

  // Get status of specific block
  getBlockStatus: (blockName) => {
    const blocks = document.querySelectorAll(`[data-block-name="${blockName}"]`);
    return Array.from(blocks).map(block => ({
      element: block,
      status: block.dataset.blockStatus,
      name: block.dataset.blockName,
      classes: block.className
    }));
  },

  

  // Force reinitialise a block

  reinitBlock: async (blockName) => {
    const blocks = document.querySelectorAll(`[data-block-name="${blockName}"]`);
    for (const block of blocks) {
      const module = await import(`/blocks/${blockName}/${blockName}.js`);
      if (module.default) await module.default(block);
    }
  },

  // Check memory usage

  getMemoryUsage: () => {
    if (performance.memory) {
      const memory = performance.memory;
      return {
        used: `${(memory.usedJSHeapSize / 1024 / 1024).toFixed(2)}MB`,
        total: `${(memory.totalJSHeapSize / 1024 / 1024).toFixed(2)}MB`,
        percentage: `${((memory.usedJSHeapSize / memory.totalJSHeapSize) * 100).toFixed(1)}%`
      };
    }
    return 'Memory API not available';
  }
};

console.log('🔧 EDS Debug Tools Available:');
console.log('- debugEDS.getBlocks()');
console.log('- debugEDS.getBlockStatus("block-name")');
console.log('- debugEDS.reinitBlock("block-name")');
console.log('- debugEDS.getMemoryUsage()');

Common Debugging Scenarios

When blocks don't appear, check if the block file exists and loads. Verify CSS class names match EDS conventions. Ensure body.appear class is present. Check for JavaScript errors in the console.

For performance issues, use instrumentation to identify bottlenecks. Monitor memory usage patterns. Check for excessive DOM mutations. Analyse async operation timing.

When dealing with integration conflicts, verify EDS attribute preservation. Check for Shadow DOM styling conflicts. Monitor race conditions between EDS and component processing. Validate error handling and recovery.

Performance Benchmarks

Based on extensive testing, here are performance targets for EDS blocks:

Block Loading: 15-20ms (including CSS/JS loading)
Block Decoration: 1-3ms for simple blocks, 5-15ms for complex blocks
Memory Overhead: <500KB per block
DOM Mutations: <15 mutations per decoration cycle

Real-World Success Story

A recent project involved a complex web component that worked perfectly in isolation but failed completely in EDS. The systematic debugging process worked like this:

Basic debugging confirmed the block was loading. Performance monitoring discovered the decoration was taking 200ms+. Instrumentation showed excessive DOM queries were the bottleneck. Optimisation cached DOM queries, reducing time to 5ms. The component worked flawlessly with 40x performance improvement.

This debugging process, which could have taken days of trial and error, was completed in under two hours.

Getting Started with EDS Debugging

Ready to master EDS debugging? Here's your action plan.

Start with basic debugging - add console logging to your blocks, implement error handling with fallbacks, monitor basic performance metrics, and set up browser console debug tools.

Move to advanced debugging by requesting AI-assisted instrumentation creation, implementing file replacement testing workflow, using comprehensive performance monitoring, and analysing memory usage and optimisation opportunities.

For professional debugging, create systematic debugging workflows, establish performance benchmarks, build automated testing procedures, and document common issues and solutions.

EDS debugging doesn't have to be mysterious. By starting with basic logging and error handling, then progressing to advanced instrumentation, you can build robust, performant blocks that work reliably in production.

The key is understanding EDS's unique architecture and using the right tools for each debugging scenario. Whether you're troubleshooting a simple styling issue or optimising complex performance bottlenecks, systematic debugging approaches will save you time and frustration.

Every expert EDS developer started with basic console.log statements. The difference is building up your debugging toolkit over time and knowing when to use each technique.

Feed this doc to your AI assistant.

Examples are here https://github.com/ddttom/webcomponents-with-eds

/fragments/ddt/proposition

style

bg-dark