refactor(v3): unify JS/CSS injection via runtime fetch

v3/UNRELEASED_CHANGELOG.md

@@ -23,6 +23,7 @@ After processing, the content will be moved to the main changelog and this file
 
 ## Fixed
 <!-- Bug fixes -->
+- Fix JS/CSS options in WebviewWindowOptions not being executed when using URL navigation (not just HTML)
 - Fix SetProcessDpiAwarenessContext "Access is denied" error when DPI awareness is already set via application manifest (#4803)
 
 ## Deprecated

v3/internal/runtime/desktop/@wailsio/runtime/src/index.ts

@@ -76,3 +76,21 @@ window._wails.handleDragLeave = handleDragLeave;
 window._wails.handleDragOver = handleDragOver;
 
 System.invoke("wails:runtime:ready");
+
+// Load optional window init scripts (fire and forget, matching current async behavior)
+// The backend identifies the window from the x-wails-window-id header
+fetch('/wails/init.js')
+    .then(r => r.ok && r.status !== 204 ? r.text() : null)
+    .then(js => { if (js) eval(js); })
+    .catch(() => {}); // Silently ignore errors
+
+fetch('/wails/init.css')
+    .then(r => r.ok && r.status !== 204 ? r.text() : null)
+    .then(css => {
+        if (css) {
+            const style = document.createElement('style');
+            style.textContent = css;
+            document.head.appendChild(style);
+        }
+    })
+    .catch(() => {}); // Silently ignore errors

v3/pkg/application/application.go

@@ -116,6 +116,50 @@
 					if err != nil {
 						result.fatal("unable to serve transport.js: %w", err)
 					}
+				case "/wails/init.js", "/wails/init.css":
+					// Serve window-specific init JS/CSS based on x-wails-window-id header
+					windowIdStr := req.Header.Get(webViewRequestHeaderWindowId)
+					if windowIdStr == "" {
+						rw.WriteHeader(http.StatusNoContent)
+						return
+					}
+					windowId, err := strconv.ParseUint(windowIdStr, 10, 64)
+					if err != nil {
+						rw.WriteHeader(http.StatusNoContent)
+						return
+					}
+
+					result.windowsLock.RLock()
+					window, exists := result.windows[uint(windowId)]
+					result.windowsLock.RUnlock()
+
+					if !exists {
+						rw.WriteHeader(http.StatusNoContent)
+						return
+					}
+
+					webviewWindow, ok := window.(*WebviewWindow)
+					if !ok {
+						rw.WriteHeader(http.StatusNoContent)
+						return
+					}
+
+					rw.Header().Set("Cache-Control", "no-cache")
+					if path == "/wails/init.js" {
+						if webviewWindow.options.JS != "" {
+							rw.Header().Set("Content-Type", "application/javascript")
+							rw.Write([]byte(webviewWindow.options.JS))
+						} else {
+							rw.WriteHeader(http.StatusNoContent)
+						}
+					} else { // init.css
+						if webviewWindow.options.CSS != "" {
+							rw.Header().Set("Content-Type", "text/css")
+							rw.Write([]byte(webviewWindow.options.CSS))
+						} else {
+							rw.WriteHeader(http.StatusNoContent)
+						}
+					}
 				default:
 					next.ServeHTTP(rw, req)
 				}

v3/pkg/application/webview_window_darwin.go

@@ -1351,15 +1351,9 @@ func (w *macosWebviewWindow) run() {
 
 		w.setURL(startURL)
 
-		// We need to wait for the HTML to load before we can execute the javascript
+		// We need to wait for the HTML to load before we can show the window
 		w.parent.OnWindowEvent(events.Mac.WebViewDidFinishNavigation, func(_ *WindowEvent) {
 			InvokeAsync(func() {
-				if options.JS != "" {
-					w.execJS(options.JS)
-				}
-				if options.CSS != "" {
-					C.windowInjectCSS(w.nsWindow, C.CString(options.CSS))
-				}
 				if !options.Hidden {
 					w.parent.Show()
 					w.setHasShadow(!options.Mac.DisableShadow)

v3/pkg/application/webview_window_linux.go

@@ -341,17 +341,6 @@ func (w *linuxWebviewWindow) run() {
 	}
 
 	w.setURL(startURL)
-	w.parent.OnWindowEvent(events.Linux.WindowLoadFinished, func(_ *WindowEvent) {
-		InvokeAsync(func() {
-			if w.parent.options.JS != "" {
-				w.execJS(w.parent.options.JS)
-			}
-			if w.parent.options.CSS != "" {
-				js := fmt.Sprintf("(function() { var style = document.createElement('style'); style.appendChild(document.createTextNode('%s')); document.head.appendChild(style); })();", w.parent.options.CSS)
-				w.execJS(js)
-			}
-		})
-	})
 
 	w.parent.RegisterHook(events.Linux.WindowLoadFinished, func(e *WindowEvent) {
 		// Inject runtime core and EnableFileDrop flag together

v3/pkg/application/webview_window_windows.go

@@ -2060,19 +2060,6 @@ func (w *windowsWebviewWindow) setupChromium() {
 	chromium.AddWebResourceRequestedFilter("*", edge.COREWEBVIEW2_WEB_RESOURCE_CONTEXT_ALL)
 
 	if w.parent.options.HTML != "" {
-		var script string
-		if w.parent.options.JS != "" {
-			script = w.parent.options.JS
-		}
-		if w.parent.options.CSS != "" {
-			script += fmt.Sprintf(
-				"; addEventListener(\"DOMContentLoaded\", (event) => { document.head.appendChild(document.createElement('style')).innerHTML=\"%s\"; });",
-				strings.ReplaceAll(w.parent.options.CSS, `"`, `\"`),
-			)
-		}
-		if script != "" {
-			chromium.Init(script)
-		}
 		chromium.NavigateToString(w.parent.options.HTML)
 	} else {
 		startURL, err := assetserver.GetStartURL(w.parent.options.URL)