in src/common/channel.js [82:95]
join: function (h, c) {
var len = c.length;
var i = len;
var f = function () {
if (!(--i)) h();
};
for (var j = 0; j < len; j++) {
if (c[j].state === 0) {
throw Error('Can only use join with sticky channels.');
}
c[j].subscribe(f);
}
if (!len) h();
},