This test checks the various use cases around sending multiple ports through MessagePort.postMessage On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS channel.port1.postMessage("same port", [channel.port1]) threw exception Error: InvalidStateError: DOM Exception 11. PASS channel.port1.postMessage("entangled port", [channel.port2]) threw exception Error: InvalidStateError: DOM Exception 11. PASS channel.port1.postMessage("null port", [channel3.port1, null, channel3.port2]) threw exception Error: InvalidStateError: DOM Exception 11. PASS channel.port1.postMessage("notAPort", [channel3.port1, {}, channel3.port2]) threw exception TypeError: Type error. PASS channel.port1.postMessage("duplicate port", [channel3.port1, channel3.port1]) threw exception Error: InvalidStateError: DOM Exception 11. PASS channel.port1.postMessage("notAnArray", channel3.port1) threw exception TypeError: Type error. PASS channel.port1.postMessage("notASequence", [{length: 3}]) threw exception TypeError: Type error. PASS channel.port1.postMessage("largeSequence", largePortArray) threw exception Error: InvalidStateError: DOM Exception 11. PASS event.ports is non-null and zero length when no port sent PASS event.ports is non-null and zero length when empty array sent PASS event.ports contains two ports when two ports sent PASS event.ports contains two ports when two ports re-sent after error PASS Sending host object has thrown Error: DataCloneError: DOM Exception 25 PASS Sending host object has thrown Error: DataCloneError: DOM Exception 25 PASS Sending Function object has thrown Error: DataCloneError: DOM Exception 25 PASS Sending Error object has thrown Error: DataCloneError: DOM Exception 25 PASS send-port: transferred one port PASS send-port-twice: transferred one port twice PASS send-two-ports: transferred two ports TEST COMPLETE