To isolate user-defined properties in the window object, you can compare the current keys of window against a "clean" iframe context. This effectively filters out all browser-native APIs and built-ins.
Here is a concise snippet you can paste directly into your console:
((win) => {
const iframe = document.createElement('iframe');
iframe.style.display = 'none';
document.body.appendChild(iframe);
const nativeProps = Object.getOwnPropertyNames(iframe.contentWindow);