// send token to iframe window.addEventListener("DOMContentLoaded", () => { const iframe = document.querySelector("iframe"); iframe.addEventListener("load", () => { iframe.contentWindow.postMessage(token, "http://localhost:8003"); }); }); // once iframe has set cookie, open WebSocket connection window.addEventListener("message", ({ origin }) => { if (origin !== "http://localhost:8003") { return; } const websocket = new WebSocket("ws://localhost:8003/"); websocket.onmessage = ({ data }) => { // event.data is expected to be "Hello !" websocket.send(`Goodbye ${data.slice(6, -1)}.`); }; runTest(websocket); });