> You're not the first person to posit that adding a new VM "almost guarantees breakage". So what? Keep the old VM, transition to the new one by specifying that's what you're targeting, then deprecate the old VM and eventually lose it altogether.
That means both VMs will be in the browser together at some point. That is a hard problem, for example because of cross-VM garbage collection (the WebKit thread where Apple refuses to accept Dart into WebKit references some papers on that).
This will cause an immediate slowdown on existing code, and a very large maintenance burden, for example you typically need to optimize fast paths in the DOM for your VM, with two VMs that is double the work, and if the VMs are allowed to communicate - and they can, if they can both access the DOM - then you have three paths to optimize now.
It's possible to migrate from one version of a language to another - say Python 2.x to 3.x. But they are not both running in the same process and communicating directly with a third shared environment like we would have on the web.
I hate to be negative about this, because as engineers we all love technical challenges. But the fact is, it's very hard to do this stuff well. (And it's even harder to standardize it.) We need to be realistic about this: Compiling into JavaScript is the only way we will see other languages on the web for the foreseeable future.
That means both VMs will be in the browser together at some point. That is a hard problem, for example because of cross-VM garbage collection (the WebKit thread where Apple refuses to accept Dart into WebKit references some papers on that).
This will cause an immediate slowdown on existing code, and a very large maintenance burden, for example you typically need to optimize fast paths in the DOM for your VM, with two VMs that is double the work, and if the VMs are allowed to communicate - and they can, if they can both access the DOM - then you have three paths to optimize now.
It's possible to migrate from one version of a language to another - say Python 2.x to 3.x. But they are not both running in the same process and communicating directly with a third shared environment like we would have on the web.
I hate to be negative about this, because as engineers we all love technical challenges. But the fact is, it's very hard to do this stuff well. (And it's even harder to standardize it.) We need to be realistic about this: Compiling into JavaScript is the only way we will see other languages on the web for the foreseeable future.