docs.sheetjs.com/docz/docs/03-demos/12-engines/21_boa.md

---
title: Rust + Boa
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---

import current from '/version.js';
import CodeBlock from '@theme/CodeBlock';

:::warning

In a production application, it is strongly recommended to use a binding for a
more performant engine like [`v8`](/docs/demos/engines/v8#rust)

:::

Boa is a pure-Rust JavaScript engine.

The [Standalone scripts](/docs/getting-started/installation/standalone) can be
parsed and evaluated in a Boa context.


## Integration Details

_Initialize Engine_

A JS context can be constructed in one line:

```rust
use boa_engine::Context;

/* initialize */
let context = &mut Context::default();
```

The following helper function evaluates strings as JS code:

```rust
use std::string::String;
use boa_engine::{Context, Source, JsError};

/* simple wrapper to evaluate code snippets */
fn eval_code(c: &mut Context, code: &str) -> Result<String, JsError> {
  let src = Source::from_bytes(code);
  match c.eval_script(src) {
    Ok(res) => { return Ok(res.to_string(c).unwrap().to_std_string_escaped()); }
    Err(e) => { return Err(e); }
  };
}
```

_Load SheetJS Scripts_

Boa provides a special helper to read source code from a path:

```rust
use std::path::Path;
use std::string::String;
use boa_engine::{Context, Source, JsError};

/* simple wrapper to evaluate an entire script file */
fn eval_file(c: &mut Context, path: &str) -> Result<String, JsError> {
  let src = Source::from_filepath(Path::new(path)).unwrap();
  match c.eval_script(src) {
    Ok(res) => { return Ok(res.to_string(c).unwrap().to_std_string_escaped()); }
    Err(e) => { return Err(e); }
  };
}

// ...
  /* load library */
  match eval_file(context, "./xlsx.full.min.js") {
    Ok(_res) => {}
    Err(e) => { return eprintln!("Uncaught {e}"); }
  }
```

To confirm the library is loaded, `XLSX.version` can be inspected:

```rust
  /* get version string */
  match eval_code(context, "XLSX.version") {
    Ok(res) => { println!( "SheetJS library version {}", res); }
    Err(e) => { return eprintln!("Uncaught {e}"); }
  }
```

### Reading Files

Boa supports `ArrayBuffer` natively.  This snippet reads data from a file into
`Vec<u8>` and stores the data as an `ArrayBuffer` in global scope:

```rust
  /* read file */
  let data: Vec<u8> = fs::read("pres.xlsx").unwrap();
  let array: JsArrayBuffer = JsArrayBuffer::from_byte_block(data, context).unwrap();
  let attrs = Attribute::WRITABLE | Attribute::ENUMERABLE | Attribute::CONFIGURABLE;
  context.register_global_property("buf", array, attrs);

  /* parse with SheetJS */
  match eval_code(context, "void (globalThis.wb = XLSX.read(buf))") {
    Ok(_res) => { }
    Err(e) => { return eprintln!("Uncaught {e}"); }
  }
```

`wb` will be a variable in the JS environment that can be inspected using the
various SheetJS API functions.

## Complete Example

:::note

This demo was tested on 2023 May 22

:::

1) Create a new project:

```bash
cargo new sheetjs-rs
cd sheetjs-rs
cargo run
```

2) Add the `boa` crate from the Git repository:

```bash
cargo add --git https://github.com/boa-dev/boa boa_engine
```

3) Download the [Standalone build](/docs/getting-started/installation/standalone):

<CodeBlock language="bash">{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}
</CodeBlock>

4) Download [`main.rs`](pathname:///boa/main.rs) and replace `src/main.rs`:

```bash
curl -L -o src/main.rs https://docs.sheetjs.com/boa/main.rs
```

5) Download [the test file](https://sheetjs.com/pres.xlsx) and run:

```bash
curl -LO https://sheetjs.com/pres.xlsx
cargo run
```

After a short wait, the contents will be displayed in CSV form.