diff --git a/source/javascripts/app/lang.js b/source/javascripts/app/lang.js
index c59a16b..2683ef3 100644
--- a/source/javascripts/app/lang.js
+++ b/source/javascripts/app/lang.js
@@ -14,6 +14,8 @@ License for the specific language governing permissions and limitations
 under the License.
 */
 (function (global) {
+  'use strict';
+
   var languages = [];
 
   global.setupLanguages = setupLanguages;
diff --git a/source/javascripts/app/search.js b/source/javascripts/app/search.js
index 8c527c7..cf2eaf8 100644
--- a/source/javascripts/app/search.js
+++ b/source/javascripts/app/search.js
@@ -1,4 +1,5 @@
 (function (global) {
+  'use strict';
 
   var $global = $(global);
   var content, darkBox, searchResults;
diff --git a/source/javascripts/app/toc.js b/source/javascripts/app/toc.js
index 779e37e..c88b67f 100644
--- a/source/javascripts/app/toc.js
+++ b/source/javascripts/app/toc.js
@@ -1,4 +1,5 @@
 (function (global) {
+  'use strict';
 
   var closeToc = function() {
     $(".tocify-wrapper").removeClass('open');