diff --git a/lib/appenders/loggly.js b/lib/appenders/loggly.js
index 8ea5ea9..23af8d7 100644
--- a/lib/appenders/loggly.js
+++ b/lib/appenders/loggly.js
@@ -1,36 +1,37 @@
 'use strict';
-var layouts = require('../layouts')
-  , loggly = require('loggly')
-  , os = require('os')
-  , passThrough = layouts.messagePassThroughLayout;
+const layouts = require('../layouts');
+const loggly = require('loggly');
+const os = require('os');
+const passThrough = layouts.messagePassThroughLayout;
 
 
 function isAnyObject(value) {
   return value !== null && (typeof value === 'object' || typeof value === 'function');
 }
 
-function numKeys(o) {
-  var res = 0;
-  for (var k in o) {
-    if (o.hasOwnProperty(k)) res++;
+/* eslint no-prototype-builtins:1,no-restricted-syntax:[1, "ForInStatement"] */
+function numKeys(obj) {
+  let res = 0;
+  for (const key in obj) {
+    if (obj.hasOwnProperty(key)) res++;
   }
   return res;
 }
 
 /**
- * @param msg - array of args for logging.
- * @returns { deTaggedMsg: [], additionalTags: [] }
+ * @param msgListArgs
+ * @returns Object{ deTaggedMsg: [...], additionalTags: [...] }
  */
 function processTags(msgListArgs) {
-  var msgList = (msgListArgs.length === 1 ? [msgListArgs[0]] : Array.apply(null, msgListArgs));
+  const msgList = (msgListArgs.length === 1 ? [msgListArgs[0]] : msgListArgs);
 
-  return msgList.reduce(function (accum, element, currentIndex, array) {
-    if (isAnyObject(element) && Array.isArray(element.tags) && numKeys(element) == 1) {
-      accum.additionalTags = accum.additionalTags.concat(element.tags);
+  return msgList.reduce((accumulate, element) => {
+    if (isAnyObject(element) && Array.isArray(element.tags) && numKeys(element) === 1) {
+      accumulate.additionalTags = accumulate.additionalTags.concat(element.tags);
     } else {
-      accum.deTaggedData.push(element);
+      accumulate.deTaggedData.push(element);
     }
-    return accum;
+    return accumulate;
   }, { deTaggedData: [], additionalTags: [] });
 }
 
@@ -38,7 +39,7 @@ function processTags(msgListArgs) {
  * Loggly Appender. Sends logging events to Loggly using node-loggly, optionally adding tags.
  *
  * This appender will scan the msg from the logging event, and pull out any argument of the
- * shape `{ tags: [] }` so that it's possibleto add tags in a normal logging call.
+ * shape `{ tags: [] }` so that it's possible to add tags in a normal logging call.
  *
  * For example:
  *
@@ -55,21 +56,21 @@ function processTags(msgListArgs) {
  * @param layout a function that takes a logevent and returns a string (defaults to objectLayout).
  */
 function logglyAppender(config, layout) {
-  var client = loggly.createClient(config);
+  const client = loggly.createClient(config);
   if (!layout) layout = passThrough;
 
-  return function (loggingEvent) {
-    var result = processTags(loggingEvent.data);
-    var deTaggedData = result.deTaggedData;
-    var additionalTags = result.additionalTags;
+  return loggingEvent => {
+    const result = processTags(loggingEvent.data);
+    const deTaggedData = result.deTaggedData;
+    const additionalTags = result.additionalTags;
 
     // Replace the data property with the deTaggedData
     loggingEvent.data = deTaggedData;
 
-    var msg = layout(loggingEvent);
+    const msg = layout(loggingEvent);
 
     client.log({
-      msg: msg,
+      msg,
       level: loggingEvent.level.levelStr,
       category: loggingEvent.categoryName,
       hostname: os.hostname().toString(),
@@ -78,13 +79,13 @@ function logglyAppender(config, layout) {
 }
 
 function configure(config) {
-  var layout;
+  let layout;
   if (config.layout) {
     layout = layouts.layout(config.layout.type, config.layout);
   }
   return logglyAppender(config, layout);
 }
 
-exports.name = 'loggly';
-exports.appender = logglyAppender;
-exports.configure = configure;
+module.exports.name = 'loggly';
+module.exports.appender = logglyAppender;
+module.exports.configure = configure;