docs.sheetjs.com/docz/docs/03-demos/42-engines/21-boa.md

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

:::danger pass

In a production application, it is strongly recommended to use a binding for a more performant engine like v8

:::

Boa is a JavaScript engine written in Rust.

SheetJS is a JavaScript library for reading and writing data from spreadsheets.

The "Complete Example" section creates a command-line tool for reading data from spreadsheets and generating CSV rows.

Integration Details

Initialize Boa

A JS context can be constructed in one line:

use boa_engine::Context;

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

The following helper function evaluates strings as JS code:

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(src) {
    Ok(res) => { return Ok(res.to_string(c).unwrap().to_std_string_escaped()); }
    Err(e) => { return Err(e); }
  };
}

Load SheetJS Scripts

The SheetJS Standalone scripts can be parsed and evaluated in a Boa context.

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

use std::path::Path;
use std::string::String;
use boa_engine::{js_string, 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(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:

  /* 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:

  /* 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(js_string!("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 Tested Deployments

This demo was tested in the following deployments:

Architecture	Boa	Date
darwin-x64	0.18.0	2024-04-25
darwin-arm	0.18.0	2024-05-23
win10-x64	0.18.0	2024-04-25
win11-arm	0.17.3	2023-12-01
linux-x64	0.18.0	2024-03-21
linux-arm	0.17.3	2023-12-01

:::

1. Create a new project:

cargo new sheetjs-boa
cd sheetjs-boa
cargo run

2. Add the boa_engine crate:

cargo add boa_engine

3. Download the SheetJS Standalone script and test file. Save both files in the project directory:

• xlsx.full.min.js
• pres.xlsx

{\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://docs.sheetjs.com/pres.xlsx}

4. Download main.rs and replace src/main.rs:

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

5. Build and run the app in release mode:

cargo run --release

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

:::caution pass

The default debug build is not optimized and can elicit stack overflow errors. It is strongly encouraged to use --release when possible.

:::