Printing is only enabled for debug builds, but that should be fine when launching directly from the editor. Do you see other log outputs from the engine (check the browser’s javascript console)? You will usually see something like this near the top.
I was testing my project and was wondering why some things are not running right in the html5 build. Looks like this is the culprit (nil properties). In the meantime, I just moved them out of go.property and just initialize with self.var as a temporary workaround.