[macspoofing]

A lot of those objections could have been applied to SPDY, a protocol google developed unilaterally and initially was only supported in Chrome and Google sites. The end result was that everybody else got a regular experience while Google Service <-> Chrome users got a better one. Other sites started including SPDY, and then browsers got in on it as well. Seemed to have worked out well.

I don't see how Dart would be any different. You can cook up worst-case hypothetical scenarios in which Dart-only sites exist because the developer was OK with cutting off half his customers, and was too lazy to generate the js output (it's not like there are vendor-specific prefixes, and even technologies like WebGL, or WebRTC that don't work universally in all browsers).

>For both of those reasons, the dart VM is somewhat worrying from the perspective of the openness of the web.

In the absolute "worst" case, Dart (an ECMA standardized language at that point) becomes very popular and forces other vendors to include a Dart VM. I'm willing to live in such a world. More likely, Dart becomes a complement to JavaScript when it comes to building RIAs in the browser (because JS is really really bad when it comes to writing and maintaining big codebases), though JS still reigns as King of the Web.

[azakai]

SPDY does have some similarities, but the differences here are very large.

As I said, Dart runs differently in the VM and in dart2js. SPDY was just not present in other browsers at first. So there wasn't a case of sites breaking in subtle and hard to debug ways in SPDY, but there is in Dart. (Later, when other browsers started to support SPDY, there were the usual spec issues, but that's a separate matter.)

The second issue I raised was that someone could ship Dart code alone, without the JS fallback. In that case, it is indeed more similar to SPDY, as someone could in principle write a SPDY-only website. Even here there is a difference, though - SPDY relies on client+server interaction. Dart is client-only (there's a Dart server, but that's not relevant here). Client-only code can more easily stay on the web for a long time, possibly forgotten and unmaintained. But this might be a small difference, so I somewhat agree with you on this point, but disagree on the previous.