AyeYaiYai

AyeYaiYai is a Rust compiler that translates a growing subset of JavaScript directly into a Preview 2 .wasm.

The repository now contains a real end-to-end baseline:

• Parse JavaScript with SWC.
• Lower supported syntax into an internal representation.
• Emit final WebAssembly bytes.
• Run the output with wasmtime.

Status

This is not close to full JavaScript yet, and it is nowhere near test262 compliance. The current compiler is intentionally narrow, but it is real and executable.

Supported today:

• let, const, and var declarations with identifier bindings
• assignment, compound assignment (+=, -=, *=, /=, %=, &&=, ||=, ??=), and ++ / --
• numeric, string, boolean, null, and undefined
• array literals, object literals, indexed access, property access, and member assignment on array/object bindings
• unary - and !
• binary +, -, *, /, %, ===, !==, <, <=, >, >=, &&, ||, ??
• ternary expressions
• top-level function declarations, parameter passing, calls, and return
• if / else
• while and for
• break and continue
• console.log(...)

Not supported yet:

• function expressions, arrow functions, closures, and captured outer variables
• nested/destructuring patterns
• general method calls and this binding
• coercive equality
• imports / exports
• exceptions
• the overwhelming majority of ECMAScript semantics required for test262

Usage

Build the compiler:

cargo build

Compile JavaScript to WASI Preview 2:

cargo run -- examples/sum.js -o sum.wasm
wasmtime sum.wasm

cargo run -- examples/control-flow.js -o control-flow.wasm
wasmtime control-flow.wasm

cargo run -- examples/objects.js -o objects.wasm
wasmtime objects.wasm

Inspect direct backend output bytes or run the resulting module:

cargo run -- examples/sum.js -o sum.wasm
hexdump -C sum.wasm

Example

function sumTo(limit) {
  let total = 0;

  for (let i = 0; i <= limit; i++) {
    if (i === 2) {
      continue;
    }

    if (i === 5) {
      break;
    }

    total += i;
  }

  return total;
}

let label = false ? "bad" : "good";
console.log(label, sumTo(10), undefined ?? "fallback");

Development

The current tests include an end-to-end integration path that compiles JavaScript, emits a Preview 2 WebAssembly component, and executes it with wasmtime:

cargo test

Run the full test262 sweep from the repository root with:

./test262.sh

You can also target high-level test262 categories directly:

./test262.sh --category language
./test262.sh --category built-ins
./test262.sh --category intl402

The wrapper will:

• use TEST262_DIR if you set it
• use TEST262_TIMEOUT_SECONDS when you want to override the per-test Wasmtime timeout, which defaults to 5
• otherwise reuse ./test262 or /tmp/test262 when present
• otherwise clone https://github.com/tc39/test262.git into ./.cache/test262
• accept repeatable --category flags for language, built-ins / builtins, intl402, annexB / annex-b, staging, and implementation-contributed
• still accept raw runner filters like --contains 'test/language/statements/' when you want a narrower subtree

At the end of the run it prints a compliance line based on discovered tests:

Compliance: <passed%> (<passed> / <discovered> discovered tests passed)
Attempt rate: <attempted%> (<attempted> / <discovered> discovered tests executed)

The full runner log is written to ./.artifacts/test262/latest.log.

Useful examples:

# Full corpus
./test262.sh

# Run a specific top-level category
./test262.sh --category language

# Run multiple categories in one sweep
./test262.sh --category language --category built-ins

# Narrow to a subtree while keeping the same reporting format
./test262.sh --contains 'test/language/statements/'

# Run a smaller sample
./test262.sh --category language --contains 'test/language/statements/with/' --limit 40

# Show the available wrapper categories
./test262.sh --list-categories