Execution order for setImmediate via postMessage is wrong:

[Yaffle]

my test, Firefox browser:

asyncTest("Execution order for setImmediate via postMessage", 1, function () {
    var orderOfExecution = '';
    var tmp = setImmediate(function () {

    });
    clearImmediate(tmp);

    window.onmessage = function (event) {
      event = event || window.event;
      if (event.data === 'some other message') {
        orderOfExecution += '1';
        if (orderOfExecution.length === 2) {
          strictEqual(orderOfExecution === '12', true, "Execution order is wrong");
          start();
        }
      }
    };
    window.postMessage('some other message', '*');

    setImmediate(function () {
      orderOfExecution += '2';
      if (orderOfExecution.length === 2) {
        strictEqual(orderOfExecution === '12', true, "Execution order is wrong");
        start();
      }
    });

});

[domenic]

You really need to be more clear as to why this is a failure of the implementation according to the spec.

Am I correct that if you do window.postMessage, then setImmediate, you are expecting the window.postMessage callback to happen before the setImmediate callback? Can you point to any spec that specifies this?

[domenic]

Furthermore, what is the point of the setImmediate/clearImmediate(tmp) at the top of the function? Without it, does the test still "fail"?

[Yaffle]

You are right, seems, according to spec, even this code:

var s = '';
window.onmessage = function (event) {
  s+= event.data;
};
for(var i = 0; i < 10; i++) {
  window.postMessage(i, '*');
}

setTimeout(function () {
  alert(s);
}, 0);

can alert different results and in Safari and Chrome postMessage actually async and doen't respect calling order .... so my test with

postMessage and setImmediate is bad

[Yaffle]

and i found another issue with execution order in Google Chrome (i have Chrome 14) :

asyncTest("Execution order test", 1, function () {
   var j = 0;
   setImmediate(function () {
     j = 1;
   });
   setTimeout(function () {
     strictEqual(!!j, true, "Execution order is wrong");
     start();
   }, 0);
});

this test works fine in all browsers, except Chrome 14,
in Chrome it fails sometimes and sometimes not...

[domenic]

The reason for that last failure is Chrome has been moving away from the HTML5 spec, which mandates that setTimeout have a minimum of 4ms (i.e. setTimeout(..., 0) should be the same as setTimeout(..., 4)). So, they are making setTimeout(..., 0) behave much like setImmediate, and I guess sometimes a Chrome-setTimeout(..., 0) gets executed even sooner than a setImmediate.

So, basically, it's Chrome's fault, and sadly there's nothing we can do about it.