Is JavaScript single threaded? If not, how do I get synchronized access to shared data?

Question

I have a web page with DIVs with a mouseover handler that is intended to show a pop-up information bubble. I don\'t want more than one info bubble

Answer 1

Here's the working version, more or less. When creating items we attach a mouseover event:

var self = this;
SimileAjax.DOM.registerEvent(labelElmtData.elmt, "mouseover", function (elt, domEvt, target) {
    return self._onHover(labelElmtData.elmt, domEvt, evt);
});

This calls a function that sets a timeout (pre-existing timeouts for a different item is cancelled first):

MyPlan.EventPainter.prototype._onHover = function(target, domEvt, evt) {            
    ... calculate x and y ...
    domEvt.cancelBubble = true;
    SimileAjax.DOM.cancelEvent(domEvt);
    this._futureShowBubble(x, y, evt);

    return false;
}
MyPlan.EventPainter.prototype._futureShowBubble = function (x, y, evt) {
    if (this._futurePopup) {
        if (evt.getID() == this._futurePopup.evt.getID()) {
            return;
        } else {
            /* We had queued a different event's pop-up; this must now be cancelled. */
            window.clearTimeout(this._futurePopup.timeoutID);
        } 
    }
    this._futurePopup = {
        x: x,
        y: y,
        evt: evt
    };    
    var self = this;
    this._futurePopup.timeoutID =  window.setTimeout(function () {
            self._onTimeout();
    }, this._popupTimeout);
}

This in turn shows the bubble if it fires before being cancelled:

MyPlan.EventPainter.prototype._onTimeout = function () {
    this._showBubble(this._futurePopup.x, this._futurePopup.y, this._futurePopup.evt);

};

MyPlan.EventPainter.prototype._showBubble = function(x, y, evt) {
    if (this._futurePopup) {
        window.clearTimeout(this._futurePopup.timeoutID);
        this._futurePopup = null;
    }        
    ...

    SimileAjax.WindowManager.cancelPopups();
    SimileAjax.Graphics.createBubbleForContentAndPoint(...);
};

This seems to work now I have set the timeout to 200 ms rather than 100 ms. Not sure why too short a timeout causes the multi-bubble thing to happen, but I guess queuing of window events or something might still be happening while the newly added elements are being laid out.