dash

ECMA-262 implementation in pure Rust.

⚠️ WIP

This is a WIP and not yet production ready. It is actively being worked on and the API is constantly changing.

Current status: Not recommended for use in real projects. Feel free to experiment. The majority of language constructs are implemented and “work fine”, many builtins are unimplemented and not tested against test262.

Goals

• Target ECMAScript 2015 and some of the newer features
• Heap/Bytecode snapshot support
• Compatibility
• Easily embeddable into any Rust application
• WebAssembly support
• JIT

Usage

Using the CLI

import * as http from '@std/http';

// We already implement Optional Typing, so you can directly annotate parameters and variables with types
// without having to use a third tool such as tsc
function* counter(start: number) {
    let num = start;
    while (true) yield num++;
}

const numbers = counter(0);
const port = 3030;

http.listen(port, (ctx) => {
    const next = numbers.next();
    ctx.respond('Request count: ' + next.value);
});

console.log('Listening on port: ' + port);

# Install Rust
$ curl -sSf https://sh.rustup.rs | sh
# Clone repo
$ git clone https://github.com/y21/dash
# Build cli
$ cd dash/cli && cargo install --path .
# Optional: rename binary to `dashjs`
$ mv ~/.cargo/bin/dash-cli ~/.cargo/bin/dashjs
# Run the program (run with --help for help)
$ dashjs run example.js

Now open up your browser, navigate to http://localhost:3030, refresh a bunch of times and see the numbers go up.

JIT

This engine has very basic support for JIT compilation. It uses LLVM for further optimizations and codegen, based on specialized type information and branches tracked by tracing one iteration of hot loops.

You can enable it by passing the jit feature flag to the dash_vm crate. Beware that it’s a very early WIP, expect bugs and crashes!

Show GIF

_{Running a silly and inefficient `isEven` function to test the performance of JS engines.} 

Embedding into a Rust application

Note that the API is not stable. Things are constantly changing, so your code may break at any time when bumping the version, which is why it is highly recommended to lock in to a specific revision for now.

• Cargo.toml

  [dependencies]
  dash_vm = { git = "https://github.com/y21/dash", features = ["eval"] }
  

  The eval feature exposes a convenience eval() method on the Vm struct that lets you specify a JavaScript source string directly.

• main.rs ```rs use dash_vm::Vm;

fn main() { let source = “const x = 42; x * x”;

let mut vm = Vm::new(Default::default());
let result = vm.eval(source, Default::default()).expect("JS Exception");

println!("Result: {}", match result {
    Value::Number(n) => n,
    _ => unreachable!()
}); } ``` <sub>See `dash-cli/` for a more detailed example</sub>

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