from playwright.sync_api import sync_playwright

with sync_playwright() as playwright:
    browser = playwright.chromium.launch(headless=False)
    try:
        page = browser.new_page()

        errors = []

        def on_web_socket(ws):
            ws.on("socketerror", lambda err: errors.append(err))

        page.on("websocket", on_web_socket)
        page.evaluate("new WebSocket('ws://localhost:8080/invalid-ws-url')")        

        print(errors)
    finally:
        browser.close()