diff --git a/src/ESPUI.cpp b/src/ESPUI.cpp
index 68b1fef..d4c8d65 100644
--- a/src/ESPUI.cpp
+++ b/src/ESPUI.cpp
@@ -17,6 +17,15 @@
 #include <umm_malloc/umm_heap_select.h>
 #endif
 
+static const char* customJS = nullptr;
+
+// Set custom JavaScript to be included in the UI.
+// js: JavaScript code as a String or C-string. Must remain valid for the lifetime of the ESPUIClass instance.
+void ESPUIClass::setCustomJS(const char* js)
+{
+    customJS = js;
+}
+
 static String heapInfo(const __FlashStringHelper* mode)
 {
     String result;
@@ -1272,6 +1281,15 @@ void ESPUIClass::begin(const char* _title, const char* username, const char* pas
         yield();
     });
 
+    server->on("/js/custom.js", HTTP_GET, [](AsyncWebServerRequest* request) {
+        if (ESPUI.basicAuth && !request->authenticate(ESPUI.basicAuthUsername, ESPUI.basicAuthPassword))
+        {
+            return request->requestAuthentication();
+        }
+
+        request->send(200, "application/javascript", customJS ? customJS : "");
+    });
+
     server->begin();
 
 #if defined(DEBUG_ESPUI)
diff --git a/src/ESPUI.h b/src/ESPUI.h
index 0e7bcc4..771b401 100644
--- a/src/ESPUI.h
+++ b/src/ESPUI.h
@@ -201,6 +201,9 @@ public:
 
     void updateVisibility(uint16_t id, bool visibility, int clientId = -1);
 
+    // Set optional global custom JavaScript to be included in the UI.
+    void setCustomJS(const char* js);
+
     // Variables
     const char* ui_title = "ESPUI"; // Store UI Title and Header Name
     Control* controls = nullptr;