I spent a morning connecting a session-recording tool to OneFindMe , the AliExpress product search engine I run in twelve languages, expecting to learn something about user behaviour. Instead it handed me a list of JavaScript errors, and every single one turned out to be a bug that had been in production for weeks while every check I had was green. That is the part worth writing down. Not the bugs — bugs are ordinary. The fact that my entire measurement apparatus was structurally incapable o...