postMessage_ports_readonly_array.htm

<!DOCTYPE html>
<title> postMessage(): read-only ports array </title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id=log></div>
<script>
"use strict";
async_test(function(t) {
  var channel = new MessageChannel();
  var targetPort = channel.port2;
  targetPort.start();
  targetPort.addEventListener("message", t.step_func_done(function(e) {
    var channel3 = new MessageChannel();
    assert_throws_js(TypeError, () => {
      e.ports.push(channel3.port1);
    }, "ports is a frozen object");
    assert_equals(e.ports.length, 1, "ports is a read only array with length == 1.");
  }), true);
  var channel2 = new MessageChannel();
  channel.port1.postMessage("ports", [channel2.port1]);
});
</script>

chromium/third_party/blink/web_tests/external/wpt/workers/postMessage_ports_readonly_array.htm