During A/B testing and conversion optimization work, third-party scripts often pollute the global window scope. This can cause conflicts, memory leaks, or unexpected behavior in your experiments. Here’s an enhanced approach to quickly identify what’s been added to the global namespace.
The Problem
When running experimentation platforms like GrowthBook, Optimizely, or Convert, you need to ensure script conflicts don’t impact your conversion metrics. The original iframe-comparison approach works, but needs better error handling and performance considerations for production environments.
Enhanced Implementation
/**
* Enhanced Window Globals Detective
* Identifies user-defined globals with performance tracking and error handling
* @param {Object} options - Configuration options
* @returns {Object} Analysis results with categorized globals
*/
const detectWindowGlobals = async (options = {}) => {
const {
includeNative = false,
excludePatterns = [],
performanceMode = true
} = options;
const startTime = performance.now();
const results = {
timing: {},
summary: {},
globals: {
functions: {},
objects: {},
arrays: {},
primitives: {},
undefined: {},
symbols: {}
},
excluded: [],
errors: []
};
try {
// Get baseline window properties using clean iframe
const iframe = document.createElement('iframe');
iframe.style.cssText = 'position:absolute;left:-9999px;top:-9999px;width:1px;height:1px;';
// Defensive iframe creation
if (!document.body) {
throw new Error('Document body not available');
}
document.body.appendChild(iframe);
// Wait for iframe to initialize properly
await new Promise(resolve => {
if (iframe.contentWindow) {
resolve();
} else {
iframe.onload = resolve;
}
});
const cleanWindow = iframe.contentWindow;
if (!cleanWindow) {
throw new Error('Failed to access iframe window');
}
// Compare current window against baseline
const currentProps = Object.getOwnPropertyNames(window);
const baselineProps = Object.getOwnPropertyNames(cleanWindow);
// Filter out baseline properties and excluded patterns
const customProps = currentProps.filter(prop =>
!baselineProps.includes(prop) &&
!excludePatterns.some(pattern =>
new RegExp(pattern).test(prop)
)
);
// Categorize properties with error handling for inaccessible properties
customProps.forEach(prop => {
try {
const value = window[prop];
const type = typeof value;
if (value === null) {
results.globals.primitives[prop] = null;
} else if (value === undefined) {
results.globals.undefined[prop] = undefined;
} else if (type === 'symbol') {
results.globals.symbols[prop] = value.toString();
} else if (type === 'function') {
results.globals.functions[prop] = {
name: value.name || 'anonymous',
length: value.length,
source: performanceMode ? '[Function]' : value.toString().slice(0, 100) + '...'
};
} else if (type === 'object') {
if (Array.isArray(value)) {
results.globals.arrays[prop] = {
length: value.length,
preview: performanceMode ? '[Array]' : value.slice(0, 3)
};
} else {
const keys = Object.keys(value);
results.globals.objects[prop] = {
constructor: value.constructor?.name || 'Unknown',
keys: performanceMode ? keys.length : keys.slice(0, 5),
preview: performanceMode ? '[Object]' : value
};
}
} else {
results.globals.primitives[prop] = value;
}
} catch (error) {
results.errors.push({ property: prop, error: error.message });
results.excluded.push(prop);
}
});
// Generate summary statistics
results.summary = {
totalWindowProps: currentProps.length,
baselineProps: baselineProps.length,
customProps: customProps.length,
functions: Object.keys(results.globals.functions).length,
objects: Object.keys(results.globals.objects).length,
arrays: Object.keys(results.globals.arrays).length,
primitives: Object.keys(results.globals.primitives).length,
errors: results.errors.length
};
// Clean up iframe
iframe.remove();
} catch (error) {
results.errors.push({ global: true, error: error.message });
}
results.timing.total = performance.now() - startTime;
return results;
};
// Usage examples
(async () => {
// Basic usage
const analysis = await detectWindowGlobals();
console.log('Custom globals detected:', analysis);
// With exclusion patterns (useful for known safe scripts)
const filtered = await detectWindowGlobals({
excludePatterns: ['^gtag', '^ga', '^dataLayer', '^_gaq']
});
console.log('Filtered analysis:', filtered);
// Performance mode off for detailed inspection
const detailed = await detectWindowGlobals({ performanceMode: false });
console.log('Detailed analysis:', detailed);
})();
Key Improvements
Async/Await Implementation: Properly handles iframe initialization instead of assuming immediate availability.
Error Boundaries: Won’t crash when encountering inaccessible properties (common with certain third-party scripts).
Performance Tracking: Measures execution time to identify potential performance impacts.
Memory Efficiency: Performance mode prevents serialization of large objects that could slow down analysis.
Pattern Exclusion: Filter out known safe globals (analytics scripts, etc.) to focus on potential problems.
Categorized Output: Groups results by type for easier debugging and analysis.
Real-World Application
This enhanced version is particularly useful when:
- Debugging script conflicts in A/B testing platforms
- Auditing third-party script impact on page performance
- Identifying memory leaks during long-running experiments
- Ensuring clean experimentation environments across different page types
The categorized output makes it easy to spot problematic patterns—like multiple conflicting analytics libraries or memory-intensive objects that could impact conversion tracking accuracy.
Happy debugging! 🔍
