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upstart writes in with a submission, via IRC, for chromas.

Mozilla Extends WebAssembly Beyond the Browser with WASI:

Mozilla’s WebAssembly started as an experiment, almost a question: is it possible to run arbitrary code in a browser without breaking the browser sandbox? A side benefit would be faster web applications that would outperform current web technologies, allowing developers to bring existing desktop applications to the web.

[...]Since its initial launch, WebAssembly has been adopted by all the major browsers, with support from Mozilla, Google, Microsoft, and Apple, who’ve all contributed code.

Best thought of as a definition of a virtual machine, WebAssembly works with the browser’s JavaScript engine to run code at speeds that compare well with native code. Instead of JavaScript’s byte code approach, it takes code written in familiar languages like C and C#, and converts it first to an assembly language-like bytecode before a final compilation as binary. WebAssembly executables are compiled before being delivered to browsers, making them a compact and efficient way of adding complex functionality to web applications.

[...]Experiments with WebAssembly outside the browser are all very well, but if it’s going to be a tool that supports cross-platform as well as cross-browser development, it needs to have new standards built around it. Mozilla recently announced the start of such an effort, with the first release of WASI: the WebAssembly System Interface.

You can perhaps consider WASI as the boundary between system level code running on the host platform and applications running in user mode.

Where WebAssembly works as an implementation of a virtual processor, WASI goes a step further and offers developers an entire conceptual operating system. With a virtual processor, there’s only one target architecture, and the JavaScript engine can handle translation between its implementation and ARM, Intel, Power, or whatever hardware you have. WASI does the same, offering WebAssembly programs its own low-level implementations of common OS functions, that are then translated into OS calls via the host JavaScript engine. Target WASI in your code, and you’re able to produce applications that run identically on macOS, on Windows, on UNIX, and more, even on mobile operating systems.

[...]It’s also important to note that you won’t be writing code that accesses the WASI interfaces directly. Instead, these will be what’s implemented in the WebAssembly equivalents of the standard libraries we use in most common languages. That way we’ll know that if we’re running a C application in WebAssembly through WASI a printf command will write to a console, no matter if it’s on Windows or UNIX. WASI implements the interfaces for WebAssembly compilers and the underlying JavaScript engine handles the actual system calls to whatever OS it’s running on. You don’t need to install the appropriate standard libraries for each target OS for your code, and you only need to compile once.

[...]There are already three implementations of WASI, Mozilla’s own implementation and a polyfill that will allow anyone to experiment with WASI in a browser. Perhaps the most interesting from a developer standpoint coming from edge delivery network Fastly. Its Lucet WebAssembly compiler is now also a runtime, with an open source release on GitHub. Currently used in Terrarium, Fastly’s experimental edge service, it’s seen as a fast alternative to JavaScript running on Google’s V8 engine.

In a blog post, Pat Hickey, a senior software engineer at Fastly, describes Lucet as able to “instantiate WebAssembly modules in under 50 microseconds, with just a few kilobytes of memory overhead. By comparison, Chromium’s V8 engine takes about 5 milliseconds, and tens of megabytes of memory overhead, to instantiate JavaScript or WebAssembly programs.”

Original Submission