diff --git a/gulpfile.js b/gulpfile.js
index 386030bfdab41b07c6d1ca793ebf09ca14282277..dea8e4b90ca1089391f3d0d45b8d104290abd817 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -99,7 +99,7 @@ var pipes = (function () {
         .pipe(cssPipe);
 
     var jsPipe = lazypipe()
-        .pipe(babel, { presets: ['es2015'] })
+        .pipe(babel, { presets: ['es2015-without-strict'], ignore: /js\/lib/ })
         .pipe(options.opt ? uglify : prettify);
 
     var twigPipe = empty;
diff --git a/package.json b/package.json
index 863a86b8d9a25a1b148550814c592001527bfc7c..36cfe47b8e9892bfd74af49ac4152f50485be283 100644
--- a/package.json
+++ b/package.json
@@ -1,9 +1,9 @@
 {
   "name": "GradeRatingSystem",
   "version": "0.0.0",
-  "dependencies": {},
   "devDependencies": {
-    "babel-preset-es2015": "^6.9.0",
+    "babel-preset-es2015": "^6.9.0", 
+    "babel-preset-es2015-without-strict": "0.0.2",
     "gulp": "^3.9.1",
     "gulp-autoprefixer": "^3.1.0",
     "gulp-babel": "^6.1.2",