text: // META: title=postMessage(): read-only ports array
  
      "use strict";
  
      var TargetPort = null;
      var description = "The postMessage() method - Make new ports into a read only array.";
  
      var t = async_test("Test Description: " + description);
  
      var channel = new MessageChannel();
  
      TargetPort = channel.port2;
      TargetPort.start();
      TargetPort.addEventListener("message", t.step_func(TestMessageEvent), true);
  
      var channel2 = new MessageChannel();
  
      channel.port1.postMessage("ports", [channel2.port1]);
  
      function TestMessageEvent(evt)
      {
          var channel3 = new MessageChannel();
          assert_throws_js(TypeError, () => {
              evt.ports.push(channel3.port1);
          }, "ports is a frozen object");
          assert_equals(evt.ports.length, 1, "ports is a read only array with length == 1.");
          t.done();
      }
  