JavaScript / AJAX Error Monitoring via Google Analytics https://developers.google.com/analytics/devguides/collection/analyticsjs/exceptions#exception_fields

js-error-signal.html

<script>
  window.addEventListener('error', function (e) {
    ga('send', 'exception', {
      exDescription: 'JavaScript Error ' + e.message + ' ' + e.filename + ': ' + e.lineno
    });
  });
  jQuery(document).ajaxError(function (e, request, settings) {
    ga('send', 'exception', {
      exDescription: 'Ajax Error ' + settings.url + ' ' + e.result
    });
  });

// V2

// Track basic JavaScript errors
window.addEventListener('error', function(e) {
    _gaq.push([
        '_trackEvent',
        'JavaScript Error',
        e.message,
        e.filename + ':  ' + e.lineno,
        true
    ]);
});

// Track AJAX errors (jQuery API)
$(document).ajaxError(function(e, request, settings) {
    _gaq.push([
        '_trackEvent',
        'Ajax error',
        settings.url,
        e.result,
        true
    ]);
});
</script>