JFG Media

The plugin catches most JS errors, logs them, and displays them in a dashboard widget.
Here are some of its features:
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Except for the plugin settings, there is no database storage involved. Log is written in a “.log” file.
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Display latest JS errors in a dashboard widget.
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Refresh errors from the dashboard widget.
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See the full error log on a separate page.
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Ignore errors if the user agent contains a specific string.
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Ignore errors if the error contains a specific string.
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Ignore errors if the script url contains a specific string.
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See which page and which script triggered the errors.
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Choose the maximum amount of errors to log per page load.
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Exclude logging errors from specific post types.
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Choose how ajax calls are made.
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<h4>Developer hooks and filters</h4>
The plugin cleans the log every 24 hours, to only keep the last 100 entries. 
You may use the “jserrlog_max_log_entries” WP filter to enable more or less entries, by returning an integer: <code>add_filter('jserrlog_max_log_entries',function(){return 200;})</code>
Alter error data: 
You may use the “jserrlog_pre_insert_error” WP filter to modify the error data before it’s inserted into the log file: <code>add_filter('jserrlog_pre_insert_error',function($error_data){return $error_data;})</code>
Trigger integrations: 
You may use the “jserrlog_after_log” WP hook to trigger an action (Slack notification, etc.) after an error was logged: <code>add_action('jserrlog_after_log',function($error_data){//do something})</code>
Backup old errors: 
You may use the “jserrlog_before_log_maintenance” WP hook to trigger an action (archive errors, etc.) before old errors are deleted: <code>add_action('jserrlog_before_log_maintenance',function($errors){//do something})</code>
<h4>Multisite</h4>
The plugin works with multisite. There’s one error log per site.

JS Error Logger

Logs front-end javascript errors, and displays them in a dashboard widget

Raygun

Raygun keeps a watchful eye on your website and notifies you of problems as they arise.
Signup for a <a href="https://app.raygun.com/signup" rel="nofollow ugc">free trial</a> of Raygun today.
Crash Reporting
<a href="https://raygun.com/platform/crash-reporting" rel="nofollow ugc">Raygun Crash Reporting</a> silently monitors your software and notifies you when users encounter errors. Crash Reporting also provides deep diagnostic information about the root cause of the error or crash, meaning your team won’t be losing valuable time digging through log files.
Using this plugin, you can enable crash reporting to track errors and exceptions generated by your WordPress site.
Real User Monitoring
Ensure your website delivers a flawless user experience using <a href="https://raygun.com/platform/real-user-monitoring" rel="nofollow ugc">Raygun Real User Monitoring</a>. Monitor the performance of every user session so you can make improvements. Measure how geographic location affects your user experience by viewing detailed breakdowns. Increase user retention by discovering the problematic pages your users get stuck on.
Using this plugin, you can enable real user monitoring to track individual user sessions, asset load times and more about your WordPress site.
Customers
Customers are why we create software. See them all, what they do, and how they’re impacted by errors, crashes, and performance issues when using your software applications. Raygun Customers gives you complete clarity on who is using your application, alongside any problems they encountered that negatively impacted their end-user experience. Understand what actions led to an issue occurring and whether the overall experience was good or bad for individual users. Customers is included in all Raygun plans and can be set up quickly by enabling it in your plugin settings.

Official provider for the Raygun Crash Reporting and Real User Monitoring services. Notifying you of errors, crashes, performance issues and more.

JS Error Logger vs Raygun