diff --git a/homeassistant/components/frontend/__init__.py b/homeassistant/components/frontend/__init__.py
index 2f64a019c19..89283b01037 100644
--- a/homeassistant/components/frontend/__init__.py
+++ b/homeassistant/components/frontend/__init__.py
@@ -322,7 +322,10 @@ def async_remove_panel(hass: HomeAssistant, frontend_url_path: str) -> None:
 
 
 def add_extra_js_url(hass: HomeAssistant, url: str, es5: bool = False) -> None:
-    """Register extra js or module url to load."""
+    """Register extra js or module url to load.
+
+    This function allows custom integrations to register extra js or module.
+    """
     key = DATA_EXTRA_JS_URL_ES5 if es5 else DATA_EXTRA_MODULE_URL
     hass.data[key].add(url)
 
diff --git a/tests/components/frontend/test_init.py b/tests/components/frontend/test_init.py
index 084db2a27d5..610e18ddcff 100644
--- a/tests/components/frontend/test_init.py
+++ b/tests/components/frontend/test_init.py
@@ -18,6 +18,7 @@ from homeassistant.components.frontend import (
     DOMAIN,
     EVENT_PANELS_UPDATED,
     THEMES_STORAGE_KEY,
+    add_extra_js_url,
     async_register_built_in_panel,
     async_remove_panel,
 )
@@ -416,6 +417,17 @@ async def test_extra_js(hass: HomeAssistant, mock_http_client_with_extra_js) ->
     assert '"/local/my_module.js"' in text
     assert '"/local/my_es5.js"' in text
 
+    # Test dynamically adding extra javascript
+    add_extra_js_url(hass, "/local/my_module_2.js", False)
+    add_extra_js_url(hass, "/local/my_es5_2.js", True)
+    resp = await mock_http_client_with_extra_js.get("")
+    assert resp.status == 200
+    assert "cache-control" not in resp.headers
+
+    text = await resp.text()
+    assert '"/local/my_module_2.js"' in text
+    assert '"/local/my_es5_2.js"' in text
+
     # safe mode
     hass.config.safe_mode = True
     resp = await mock_http_client_with_extra_js.get("")
@@ -426,6 +438,17 @@ async def test_extra_js(hass: HomeAssistant, mock_http_client_with_extra_js) ->
     assert '"/local/my_module.js"' not in text
     assert '"/local/my_es5.js"' not in text
 
+    # Test dynamically adding extra javascript
+    add_extra_js_url(hass, "/local/my_module_2.js", False)
+    add_extra_js_url(hass, "/local/my_es5_2.js", True)
+    resp = await mock_http_client_with_extra_js.get("")
+    assert resp.status == 200
+    assert "cache-control" not in resp.headers
+
+    text = await resp.text()
+    assert '"/local/my_module_2.js"' not in text
+    assert '"/local/my_es5_2.js"' not in text
+
 
 async def test_get_panels(
     hass: HomeAssistant, hass_ws_client: WebSocketGenerator, mock_http_client