Limit the rate of pinging frontend error to 1 ping every 5 seconds (#92)

app/static/pages/app.js

@@ -119,6 +119,8 @@ oppiaFoundationWebsite.constant(
 // Overwrite the built-in exceptionHandler service to log errors to the backend
 // (so that they can be fixed).
 oppiaFoundationWebsite.factory('$exceptionHandler', ['$log', function($log) {
+  var MIN_TIME_BETWEEN_ERRORS_MSEC = 5000;
+  var timeOfLastPostedError = Date.now() - MIN_TIME_BETWEEN_ERRORS_MSEC;
   return function(exception, cause) {
     var messageAndSourceAndStackTrace = [
       '',
@@ -127,25 +129,30 @@ oppiaFoundationWebsite.factory('$exceptionHandler', ['$log', function($log) {
       String(exception.stack),
       '    at URL: ' + window.location.href
     ].join('\n');
-    // Catch all errors, to guard against infinite recursive loops.
-    try {
-      // We use jQuery here instead of Angular's $http, since the latter
-      // creates a circular dependency.
-      $.ajax({
-        type: 'POST',
-        url: '/ajax/frontend_errors',
-        data: $.param({
-          payload: JSON.stringify({
-            error: messageAndSourceAndStackTrace
-          }),
-          source: document.URL
-        }, true),
-        dataType: 'text',
-        async: true
-      });
-    } catch (loggingError) {
-      $log.warn('Error logging failed.');
+
+    // Throttle to at most 1 backend ping every MIN_TIME_BETWEEN_ERRORS_MSEC.
+    if (Date.now() - timeOfLastPostedError > MIN_TIME_BETWEEN_ERRORS_MSEC) {
+      // Catch all errors, to guard against infinite recursive loops.
+      try {
+        // We use jQuery here instead of Angular's $http, since the latter
+        // creates a circular dependency.
+        $.ajax({
+          type: 'POST',
+          url: '/ajax/frontend_errors',
+          data: $.param({
+            payload: JSON.stringify({
+              error: messageAndSourceAndStackTrace
+            }),
+            source: document.URL
+          }, true),
+          dataType: 'text',
+          async: true
+        });
+      } catch (loggingError) {
+        $log.warn('Error logging failed.');
+      }
     }
+
     $log.error.apply($log, arguments);
   };
 }]);