diff --git a/lib/output/index.js b/lib/output/index.js
index e8f45f3..f4eb9bb 100644
--- a/lib/output/index.js
+++ b/lib/output/index.js
@@ -1,6 +1,8 @@
-var path = require('path')
-var fs = require('graceful-fs')
-var mkdir = require('../mkdirs')
+'use strict'
+
+const fs = require('graceful-fs')
+const path = require('path')
+const mkdir = require('../mkdirs')
 
 function outputFile (file, data, encoding, callback) {
   if (typeof encoding === 'function') {
@@ -8,11 +10,11 @@ function outputFile (file, data, encoding, callback) {
     encoding = 'utf8'
   }
 
-  var dir = path.dirname(file)
-  fs.exists(dir, function (itDoes) {
+  const dir = path.dirname(file)
+  fs.exists(dir, itDoes => {
     if (itDoes) return fs.writeFile(file, data, encoding, callback)
 
-    mkdir.mkdirs(dir, function (err) {
+    mkdir.mkdirs(dir, err => {
       if (err) return callback(err)
 
       fs.writeFile(file, data, encoding, callback)
@@ -21,7 +23,7 @@ function outputFile (file, data, encoding, callback) {
 }
 
 function outputFileSync (file, data, encoding) {
-  var dir = path.dirname(file)
+  const dir = path.dirname(file)
   if (fs.existsSync(dir)) {
     return fs.writeFileSync.apply(fs, arguments)
   }
@@ -30,6 +32,6 @@ function outputFileSync (file, data, encoding) {
 }
 
 module.exports = {
-  outputFile: outputFile,
-  outputFileSync: outputFileSync
+  outputFile,
+  outputFileSync
 }