I can't see a property on Safari after add an script on WKWebView

After insert this script I can't see the property window.app.isNative = true on Safari, What I'm missing here? Thanks in advance

userContentController.addUserScript(WKUserScript(source: """function() {

    if (!window.app) {

           window.app = {};

                      }

              window.app.isAndroid = false;

              window.app.isIOS = true;

              window.app.isNative = true;

              originWhitelist={['*']}

      }

""", injectionTime: .atDocumentStart, forMainFrameOnly: true))