diff --git a/lib/Parser/LL/JS.hs b/lib/Parser/LL/JS.hs
index b2e78f4..c6e4c4a 100644
--- a/lib/Parser/LL/JS.hs
+++ b/lib/Parser/LL/JS.hs
@@ -22,6 +22,8 @@ instance ParserWriter LLParser JS where
     where
     basename = parserOptionsBaseFileName
     sourceFile = [interp|
+'use strict'
+
 const {TokenType, tokToStr} = require('./lexer.js')
 #{topTop gtop}
 const NonTerminal = {
diff --git a/lib/Parser/LR/JS.hs b/lib/Parser/LR/JS.hs
index c287a0c..37807da 100644
--- a/lib/Parser/LR/JS.hs
+++ b/lib/Parser/LR/JS.hs
@@ -24,6 +24,8 @@ instance LRPoint p => ParserWriter (LRParser p) JS where
   --writeParser :: Proxy lang -> Text -> ParserOptions a -> parser -> [(FilePath,Text)]
   writeParser _ gtop ParserOptions{..} LRParser{..} = [
       (base <> ".js", [interp|
+'use strict'
+
 const {TokenType, tokToStr} = require('./lexer.js')
 
 #{topTop gtop}
diff --git a/lib/Parser/Recursive/JS.hs b/lib/Parser/Recursive/JS.hs
index 03a806c..dafcccb 100644
--- a/lib/Parser/Recursive/JS.hs
+++ b/lib/Parser/Recursive/JS.hs
@@ -22,6 +22,8 @@ import Parser.Recursive.Build
 instance ParserWriter RecursiveParser JS where
   writeParser _ gtop ParserOptions{..} RecursiveParser{..} =
     [(basename <> ".js", [interp|
+'use strict'
+
 const {tokToStr, TokenType} = require('./lexer.js')
 #{topTop gtop}
 class #{parserOptionsName}#{topInh gtop} {