How to fix Promise rejection `$a`

A new variant of Google Translate errors has emerged, appearing as unhandled promise rejections with the cryptic message “$a”. Unlike other Google Translate errors that provide some context, this one is particularly mysterious due to iOS’s aggressive stack trace sanitization.

The Error

The error will be recorded as:

Unhandled Promise Rejection: $a

With a completely sanitized stack trace on iOS devices showing only:

@
wj@
@

What’s Actually Happening

This “$a” error represents an unhandled promise rejection within Google Translate’s minified code. The single “$a” identifier is a minified variable or error message that Google’s translation service throws when encountering asynchronous processing failures.

Key characteristics:

• Appears as a promise rejection, not a standard JavaScript error
• Predominantly affects iOS browsers (Safari, Chrome for iOS, Google App)
• Firefox occasionally shows it with visible Google Translate references
• iOS completely sanitizes the stack trace to meaningless symbols

The critical difference from other Google Translate errors is that this is an unhandled promise rejection, meaning Google’s code isn’t properly catching errors in their async operations.

Understanding the Root Cause

Promise Rejection vs Regular Errors

Traditional Google Translate errors like “undefined is not an object” are synchronous failures. The “$a” error is different—it’s an asynchronous promise that Google’s code rejected without a proper catch handler:

// Simplified representation of what's happening in Google's code
async function translateOperation() {
  // Some async operation fails
  throw new Error("$a"); // Minified error
  // No catch handler = unhandled rejection
}

iOS Stack Trace Sanitization

iOS browsers aggressively sanitize stack traces from third-party scripts for privacy reasons. What starts as meaningful debugging information gets reduced to:

• @ - Anonymous function calls
• wj@ - Minified function name (varies)
• No file names, line numbers, or URLs

This makes it impossible to trace the error back to specific Google Translate operations, even though Firefox users might see the full translate.googleapis.com source.

Why Promise Rejections Matter

Unhandled promise rejections trigger the global unhandledrejection event, which many error monitoring tools capture. Unlike regular errors that might be caught and handled, these rejections always bubble up to your error monitoring.

How to Fix Unhandled Promise Rejection “$a”

Since this error originates from Google’s service, you can’t fix the root cause. Instead, focus on filtering and handling it appropriately:

Configure Error Monitoring to Ignore Google Translate Errors

Configure your error monitoring service to filter these patterns:

TrackJS Configuration:

• Error message equals: $a
• Stack trace contains: wj@ (for iOS patterns)
• Error type: unhandledrejection

For browsers showing more detail:

• URL contains: translate.googleapis.com
• Stack trace contains: /_/translate_http/_/js/

Debugging iOS Sanitized Stack Traces

The sanitized iOS stack traces make debugging nearly impossible, but you can use these strategies:

Correlation Analysis

Look for patterns in when these errors occur:

• During page load (translation initialization)
• After user interactions (manual translation triggers)
• Specific pages or content types

User Agent Patterns

Track which iOS versions and browsers are most affected to understand the scope of the issue.

Monitor Real Application Errors

Don’t let Google Translate noise obscure actual application issues. Error monitoring services like TrackJS can automatically filter out these third-party service errors while capturing real promise rejections from your code.

Without proper filtering, these “$a” errors can flood your error logs, making it difficult to spot genuine application problems. Professional error monitoring helps you maintain signal clarity by separating third-party noise from actionable application errors.

When These Errors Matter

While generally safe to ignore, investigate if you notice:

Correlation with functionality issues:

• Translation features stop working when errors appear
• Page functionality breaks during translation
• Users report translation-related problems

Unusual patterns:

• Sudden spike in “$a” errors across all users
• Errors only on specific pages or features
• Correlation with your deployment timeline

Summary

The unhandled promise rejection “$a” is Google Translate’s latest contribution to error log noise. Its unique characteristics—being a promise rejection with sanitized iOS stack traces—make it particularly annoying for developers trying to maintain clean error monitoring.

The error represents async failures within Google’s translation service and cannot be fixed from your application. The solution is strategic filtering: ignore the “$a” pattern while maintaining visibility into real application promise rejections. Focus on errors you can actually fix rather than chasing ghosts in Google’s minified code.