chromium/third_party/blink/web_tests/external/wpt/websockets/multi-globals/support/incumbent.sub.html

<!DOCTYPE html>
<title>Incumbent page used as a test helper</title>

<iframe src="relevant.html" id="r"></iframe>

<script>
"use strict";

const relevant = document.querySelector("#r").contentWindow;

window.setupWebSocket = (binaryType, fn) => {
    const wsocket = new relevant.WebSocket("ws://{{host}}:{{ports[ws][0]}}/echo");

    wsocket.addEventListener("open", () => {
        wsocket.binaryType = binaryType;
        wsocket.send(new ArrayBuffer(15));
    });

    wsocket.addEventListener("message", ev => {
        fn(relevant, ev);
    });
};

</script>