That talk on which Axel Rauschmayer reported had some info from a presentation given by Andreas Rossberg of the V8 team to the last TC39 meeting. Here's the PDF

That talk on which Axel Rauschmayer reported had some info from a presentation given by Andreas Rossberg of the V8 team to the last TC39 meeting. Here's the PDF: http://www.mpi-sws.org/~rossberg/papers/JSExperimentalDirections.pdf http://www.mpi-sws.org/~rossberg/papers/JSExperimentalDirect... There are two ideas: 1. A `"use stricter";` (originally "use sanity" :-/) prologue directive that would not change runtime semantics for code that passed all of static checks, (control flow dependent) dynamic exception-throwing tests, and runtime restrictions on object behavior. 2. A "SoundScript" mode, perhaps enabled by a `use types;` opt-in, or expressed some other way (per module?), that enables gradual type checking based on optional annotations inspired by TypeScript, but with TS-incompatible differences. Mode 1 might fly with TC39, because it does not fork semantics for code that passes all checks. But for real-world code, there will be divergence when run on old vs. new browsers, so I expect push-back in TC39 on this mode being expressed by a useless string expression statement. Mode 2 cannot be enabled by a fake-string-expression-statement "prologue directive".