[dangoor]

TC39 explicitly rejected this sort of approach a few years ago, because of the unpleasant way it would fork the web. They _did_ automatically clean up some behavior in a module context when you knew you were using a modern JS engine, but they kept that to a minimum.

Unfortunately, I couldn't find any links to articles written at the time about this, but they definitely did consider "use" options or script type="es2021" kinds of options.

[arp242]

I can see where they're coming from; backwards compatibility is often a hard problem, and this is no exception. But the downside of this approach is that we'll be living with these sort of backward-compatible hacks for decades to come :-/

Imagine learning JS in 5 years: "you can index arrays with subscripts, but actually, if you want to get negative indexes you need to use .at()"

vs.

"Always add 'use es2021'; at the top of your scripts. You can index arrays with subscripts."

I'm hardly a huge Perl fan, but their approach made a lot more sense IMHO and is a good trade-off between making sure existing code works, and not complicating the language for future use. The "fork" (which seems a bit hyperbolic to me) is a very minor short-term pain at best for significant long-term gains.

I don't know of any other mainstream language that's so conservative as JavaScript in never breaking anything, even optionally with flags.

Besides, compatibility is important but not holy. Some programs probably also rely on "[9] * 2" resulting in Number 18, but we really ought to fix that (with or without flag) IMHO because these sort of gotchas result in people writing bugs every single day where it works for an array length of 1 and then it has 2 values and you get NaN. The pain of breaking backwards compatibility is minor compared to the pain of new bugs being created every single day.

Golden opportunities are being missed here, and it's a shame.

[hutrdvnj]

I see two scenarios for ES2042 (possibly both).

0. It will end up completely unnoticed, because everyone is using any language you like and compiles to web assembly, which is the defacto standard for more than a decade.

1. It's like a new C++, because of the many TC39 stage 3 proposals that has been added over the years without the possibility to ever fix the language in order to not fork the web.