It might give different tooling output, but the tooling wouldn’t break. Likewise, the only side effect of the code itself is that some of it would get faster be

It might give different tooling output, but the tooling wouldn’t break. Likewise, the only side effect of the code itself is that some of it would get faster because functions wouldn’t need to return. The percentage of sites affected by automated stack tools is far less than the number of other sites that would benefit from tail calls. More importantly, this breakage already happened 8 YEARS ago in Safari and 20% of all web users already break those expectations, so companies should have already adjusted. At this point, it only serves to split the web.