Short-circuits, innocent code and nsIDOMEvent targets

An user on AMI tells me that my bonsai RichFeedButton doesn’t work when installed together with another extension.

I install the offended extension and discover that RichFeedButton breaks this little jewel!

The solution was simple but the bug hunting was hard

The problem was into an innocent function associated with a listener that simply checks the nsIDOMEvent’s target id and attrName as shown below
if (event.target.id == "xxx" && event.attrName == "yyy") {
...
}

For some motivations the “event.target” expression breaks the other extension.

I suspect event.target at some event stage isn’t valid and generates internally some error corrupting (???) the full event queue or simply I’m a bad programmer

The solution??

Simply swaps first equality test with second one

if (event.attrName == "yyy" && event.target.id == "xxx") {
...
}

The javascript short-circuit evaluation ensures me event.target.id is parsed only if first condition is true.

Every day I learn something about XUL and its implementation…