Boa is an experimental JavaScript lexer, parser and interpreter written in Rust 🦀, it has support for **more** than 90% of the latest ECMAScript specification. We continuously improve the conformance to keep up with the ever-evolving standard.
[![Build Status][build_badge]][build_link]
[](https://codecov.io/gh/boa-dev/boa)
[](https://crates.io/crates/boa_engine)
[](https://docs.rs/boa_engine)
[](https://discord.gg/tUFFk9Y)
[](https://matrix.to/#/#boa:matrix.org)
[build_badge]: https://github.com/boa-dev/boa/actions/workflows/rust.yml/badge.svg?event=push&branch=main
[build_link]: https://github.com/boa-dev/boa/actions/workflows/rust.yml?query=event%3Apush+branch%3Amain
## ⚡️ Live Demo (WASM)
Try out the engine now at the live WASM playground [here](https://boajs.dev/playground)!
Prefer a CLI? Feel free to try out `boa_cli`!
## 📦 Crates
Boa currently publishes and actively maintains the following crates:
- **`boa_ast`** - Boa's ECMAScript Abstract Syntax Tree
- **`boa_cli`** - Boa's CLI && REPL implementation
- **`boa_engine`** - Boa's implementation of ECMAScript builtin objects and
execution
- **`boa_gc`** - Boa's garbage collector
- **`boa_interner`** - Boa's string interner
- **`boa_parser`** - Boa's lexer and parser
- **`boa_icu_provider`** - Boa's ICU4X data provider
- **`boa_runtime`** - Boa's WebAPI features
- **`boa_string`** - Boa's ECMAScript string implementation.
- **`tag_ptr`** - Utility library that enables a pointer to be associated with a tag of type `usize`.
> [!NOTE]
>
> The `Boa` and `boa_unicode` crates are deprecated.
## 🚀 Example
To start using Boa simply add the `boa_engine` crate to your `Cargo.toml`:
```toml
[dependencies]
boa_engine = "0.20.0"
```
Then in `main.rs`, copy the below:
```rust
use boa_engine::{Context, Source, JsResult};
fn main() -> JsResult<()> {
let js_code = r#"
let two = 1 + 1;
let definitely_not_four = two + "2";
definitely_not_four
"#;
// Instantiate the execution context
let mut context = Context::default();
// Parse the source code
let result = context.eval(Source::from_bytes(js_code))?;
println!("{}", result.display());
Ok(())
}
```
Now, all that's left to do is `cargo run`.
Congrats! You've executed your first JavaScript code using Boa!
## 🔎 Documentation
For more information on Boa's API, feel free to check out our documentation.
[**API Documentation**](https://docs.rs/boa_engine/latest/boa_engine/)
## 🏅 Conformance
To know more details about Boa's conformance surrounding the _ECMAScript_ specification,
you can check out our _ECMASCript Test262_ test suite results [here](https://boajs.dev/conformance).
## 🪚 Contributing
Please, check the [CONTRIBUTING.md](CONTRIBUTING.md) file to know how to
contribute in the project. You will need Rust installed and an editor. We have
some configurations ready for VSCode.
### 🐛 Debugging
Check [debugging.md](./docs/debugging.md) for more info on debugging.
### 🕸 Web Assembly
> [!IMPORTANT]
>
> This only applies to `wasm32-unknown-unknown` target,
> `WASI` and `Emscripten` target variants are handled automatically.
- Enable the `js` feature flag.
- Set `RUSTFLAGS='--cfg getrandom_backend="wasm_js"'`
The `rustflags` can also be set by adding a `.cargo/config.toml` file in the project root directory:
```toml
[target.wasm32-unknown-unknown]
rustflags = '--cfg getrandom_backend="wasm_js"'
```
For more information see: [`getrandom` WebAssembly Support][getrandom-webassembly-support]
[getrandom-webassembly-support]: https://docs.rs/getrandom/latest/getrandom/index.html#webassembly-support
## ⚙️ Usage
- Clone this repo.
- Run with `cargo run -- test.js` in the project root directory where `test.js` is a path to an existing JS file with any valid JS code.
- If any JS doesn't work then it's a bug. Please raise an [issue](https://github.com/boa-dev/boa/issues/)!
### Example
### Command-line Options
```txt
Usage: boa [OPTIONS] [FILE]...
Arguments:
[FILE]... The JavaScript file(s) to be evaluated
Options:
--strict Run in strict mode
-a, --dump-ast [] Dump the AST to stdout with the given format [possible values: debug, json, json-pretty]
-t, --trace Dump the AST to stdout with the given format
--vi Use vi mode in the REPL
-O, --optimize
--optimizer-statistics
--flowgraph [] Generate instruction flowgraph. Default is Graphviz [possible values: graphviz, mermaid]
--flowgraph-direction Specifies the direction of the flowgraph. Default is top-top-bottom [possible values: top-to-bottom, bottom-to-top, left-to-right, right-to-left]
--debug-object Inject debugging object `$boa`
-m, --module Treats the input files as modules
-r, --root Root path from where the module resolver will try to load the modules [default: .]
-h, --help Print help (see more with '--help')
-V, --version Print version
```
## 🧭 Roadmap
See [Milestones](https://github.com/boa-dev/boa/milestones).
## 📊 Benchmarks
The current benchmarks are taken from v8's benchmark that you can find [here][boa-benchmarks]. You can also view the results of nightly benchmark runs comparing Boa with other JavaScript engines [here](https://boajs.dev/benchmarks).
If you wish to run the benchmarks locally, then run Boa in release using the `combined.js` script which contains all the sub-benchmarks in the `bench-v8` directory.
```bash
cargo run --release -p boa_cli -- bench-v8/combined.js
```
> [!TIP]
>
> If you'd like to run only a subset of the benchmarks, you can modify the `Makefile` located in the [`bench-v8` directory][boa-benchmarks].
> Comment out the benchmarks you don't want to include, then run `make`. After that, you can run Boa using the same command as above.
[boa-benchmarks]: https://github.com/boa-dev/data/tree/benchmarks/bench
## 🧠 Profiling
See [Profiling](./docs/profiling.md).
## 📆 Changelog
See [CHANGELOG.md](./CHANGELOG.md).
## 💬 Communication
Feel free to contact us on [Matrix](https://matrix.to/#/#boa:matrix.org) if you have any questions.
Contributor discussions take place on the same Matrix Space if you're interested in contributing.
We also have a [Discord](https://discord.gg/tUFFk9Y) for any questions or issues.
## ⚖️ License
This project is licensed under the [Unlicense](./LICENSE-UNLICENSE) or [MIT](./LICENSE-MIT) licenses, at your option.
