diff --git a/src/accounting/static/js/account-form.js b/src/accounting/static/js/account-form.js
index da8b38a..0c63919 100644
--- a/src/accounting/static/js/account-form.js
+++ b/src/accounting/static/js/account-form.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/1
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/account-order.js b/src/accounting/static/js/account-order.js
index 5ab38d9..ef61cf7 100644
--- a/src/accounting/static/js/account-order.js
+++ b/src/accounting/static/js/account-order.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/2
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/account-selector.js b/src/accounting/static/js/account-selector.js
index 7ac0ae1..2268371 100644
--- a/src/accounting/static/js/account-selector.js
+++ b/src/accounting/static/js/account-selector.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/28
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/currency-form.js b/src/accounting/static/js/currency-form.js
index b87b342..d303e64 100644
--- a/src/accounting/static/js/currency-form.js
+++ b/src/accounting/static/js/currency-form.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/6
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/drag-and-drop-reorder.js b/src/accounting/static/js/drag-and-drop-reorder.js
index e7191d6..c766c04 100644
--- a/src/accounting/static/js/drag-and-drop-reorder.js
+++ b/src/accounting/static/js/drag-and-drop-reorder.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/3
  */
+"use strict";
 
 /**
  * Initializes the drag-and-drop reordering on a list.
diff --git a/src/accounting/static/js/material-fab-speed-dial.js b/src/accounting/static/js/material-fab-speed-dial.js
index 0b3ebf7..43bca85 100644
--- a/src/accounting/static/js/material-fab-speed-dial.js
+++ b/src/accounting/static/js/material-fab-speed-dial.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/25
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/period-chooser.js b/src/accounting/static/js/period-chooser.js
index 3cf0c65..faa4f8f 100644
--- a/src/accounting/static/js/period-chooser.js
+++ b/src/accounting/static/js/period-chooser.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/3/4
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/summary-editor.js b/src/accounting/static/js/summary-editor.js
index b43ac0e..9d25e3c 100644
--- a/src/accounting/static/js/summary-editor.js
+++ b/src/accounting/static/js/summary-editor.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/28
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/transaction-form.js b/src/accounting/static/js/transaction-form.js
index 13e25c6..f882e9d 100644
--- a/src/accounting/static/js/transaction-form.js
+++ b/src/accounting/static/js/transaction-form.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/25
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {
diff --git a/src/accounting/static/js/transaction-order.js b/src/accounting/static/js/transaction-order.js
index a92cb8c..be8e29d 100644
--- a/src/accounting/static/js/transaction-order.js
+++ b/src/accounting/static/js/transaction-order.js
@@ -20,6 +20,7 @@
 /* Author: imacat@mail.imacat.idv.tw (imacat)
  * First written: 2023/2/26
  */
+"use strict";
 
 // Initializes the page JavaScript.
 document.addEventListener("DOMContentLoaded", () => {