yield www problems in javascript

I'm having almost the exact same problem as this other post http://answers.unity3d.com/questions/38753/yield-return-www-not-returning, except I'm using Javascript. In a nutshell I'm doing this (the url is way simplified for this example):

function PostScore(score:int)
{
    var www:WWW = new WWW(myScoreURL + "?value=" + score);

    yield www;
}

Nothing happens.

However, if I replace yield www with this, it works in debug mode, but outright crashes web browsers.

while (www.isDone == false)
{
    // Wait
}

If I throw a yield in the middle of the while loop, then nothing happens again.