diff --git a/share/pdf2htmlEX.js.in b/share/pdf2htmlEX.js.in
index 2a363e4..e157418 100644
--- a/share/pdf2htmlEX.js.in
+++ b/share/pdf2htmlEX.js.in
@@ -6,6 +6,8 @@
* Copyright 2012,2013 Lu Wang
*/
+'use strict';
+
var pdf2htmlEX = (function(){
var CSS_CLASS_NAMES = {
page_frame : '@CSS_PAGE_FRAME_CN@',