diff --git a/src/helper/enum.js b/src/helper/enum.js
index cbaee8d..58ed659 100644
--- a/src/helper/enum.js
+++ b/src/helper/enum.js
@@ -1,3 +1,4 @@
+"use strict";
 class Juicescript_helper_enum {
 	constructor(...keys){
 		keys.forEach((key, i) => {
diff --git a/src/io.js b/src/io.js
index a87b352..17320a2 100644
--- a/src/io.js
+++ b/src/io.js
@@ -1,3 +1,4 @@
+"use strict";
 class Juicescript_io {
 	/*
 		CONSTRUCTOR: Return new juicescript io adapter with CALLBACKs
diff --git a/src/lexer.js b/src/lexer.js
index 38223ca..7c155d5 100644
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -1,3 +1,4 @@
+"use strict";
 class Juicescript_lexer {
 	/*
 		CONSTRUCTOR: Return new juicescript lexer for SOURCE with OPTIONS
diff --git a/src/main.js b/src/main.js
index 362e5c6..8dcd378 100644
--- a/src/main.js
+++ b/src/main.js
@@ -1,3 +1,4 @@
+"use strict";
 class Juicescript {
 	// TOKEN TYPES //
 	static token_type = new Juicescript_helper_enum(