> If you're right, and can land optional types and bignums soon,

First, "soon" is incremental and staged, so it's not as though full optional types won't take till 2020 to be "landed" as in standardized and widely implemented.

Second, the only way to get to that 2020 is by working in TC39 now, 2015, as SoundScript is. Not pulling a Dart in 2010, doing a different language and VM, making a disjoint Ecma standard, and then hoping to pull off a last minute rendezvous.

> then Dart's semantics can become a subset of ECMAScript.

They cannot, without incompatible changes. This doesn't fit your "big investment now for great tooling, easy migration later" thinking for Dart, and it's right out for JS.

Problems go beyond bignums, but just bignums are enough. Dart can start a counter at 0 and ++ it past 2^53 without loss of precision. JS can't (you'd have to use bignum(0) or 0n). Something's got to give, and it looks likely to be infeasible to statically analyze and auto-fix all the code.

> At this point it's pretty easy to replace the Dart language in the VM to support the ECMAScript syntax subset, and source code translate the core libraries over to ECMAScript. Then you have a fast VM which supports an easily optimisable subset of ECMAscript, and a large class library. This still seems like a good outcome to me.

Except that this won't happen in 2020 thanks to Dart, because it forked hard early. Instead we will get to 2020 (maybe 2018) with SoundScript standardized, still incompatible with Dart, and no good outcome for Dart users who can't get dart2js to perform as well as DartVM. But in this scenario there's likely little market pressure on browsers to do the crazy amount of work to support multiple VMs. Good outcome?

Worse, this is a narrow, self-interested point of view from Dart side. What about the JS side? Why should we have waited five years at least to get to SoundScript? How much sooner from 2010 or even 2015 could we get to the promised land if Dart weren't flying off toward Pluto?

> "any real-world usage data from it are nowhere"

> Ignoring available data from existing optionally typed VMs during the standardisation process doesn't seem like a smart idea.

Cut the bad-faith arguing, please. It's not up to me to find Dart's "data" (where is it available, pray tell?) and try to separate all the confounding variables arising from Dart being a different VM and language.

Sound/StrongScript in V8, OTOH, will give unconfounded data this year, in the context of JS and TC39.

Who are you gonna bet on? Anyway, leave me out of it, try begging some Dart staffer for "data".

> Anyway, I hope there is good discussion at TC39 about Nominal typing with implicit interfaces, vs Structural typing. I'm not really a fan of structural typing - I think the Dart team made the right call here.

Did you read the StrongScript slides? Try http://www.mpi-sws.org/~rossberg/papers/JSExperimentalDirect... or better location.

> > Alan Kay was right, the best way to predict is to invent.

> You mean to invent something compatible with legacy technology and easily adopted ;)

That's right, because of noted non-flamebait minor premise: JS cannot be replaced. Are you going to argue against this forthrightly? I thought not!