Crate boa_engine

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Boa’s boa_engine crate implements ECMAScript’s standard library of builtin objects and an ECMAScript context, bytecompiler, and virtual machine for code execution.

§Example usage

You can find multiple examples of the usage of Boa in the boa_examples crate. In order to use Boa in your project, you will need to add the boa_engine crate to your Cargo.toml file. You will need to use a Source structure to handle the JavaScript code to execute, and a Context structure to execute the code:

use boa_engine::{Context, Source};

let js_code = r#"
    let two = 1 + 1;
    let definitely_not_four = two + "2";


// Instantiate the execution context
let mut context = Context::default();

// Parse the source code
match context.eval(Source::from_bytes(js_code)) {
    Ok(res) => {
            res.to_string(&mut context).unwrap().to_std_string_escaped()
    Err(e) => {
        // Pretty print the error
        eprintln!("Uncaught {e}");

§Crate Features

  • serde - Enables serialization and deserialization of the AST (Abstract Syntax Tree).
  • profiler - Enables profiling with measureme (this is mostly internal).
  • intl - Enables boa’s ECMA-402 Internationalization API (Intl object)

§About Boa

Boa is an open-source, experimental ECMAScript Engine written in Rust for lexing, parsing and executing ECMAScript/JavaScript. Currently, Boa supports some of the language. More information can be viewed at Boa’s website.

Try out the most recent release with Boa’s live demo playground.

§Boa Crates



  • Boa’s implementation of ECMAScript’s bigint primitive type.
  • Boa’s ECMAScript built-in object implementations, e.g. Object, String, Math, Array, etc.
  • This module contains the bytecode compiler.
  • Traits and structs for implementing native classes.
  • The ECMAScript context.
  • Boa’s implementation of ECMAScript’s Environment Records.
  • Error-related types and conversions.
  • Boa’s API to create and customize ECMAScript jobs and job queues.
  • Boa’s implementation of the ECMAScript’s module system.
  • Boa’s wrappers for native Rust functions to be compatible with ECMAScript calls.
  • Boa’s representation of a JavaScript object and builtin object wrappers
  • Implements optimizations.
  • A convenience module that re-exports the most commonly-used Boa APIs
  • Boa’s implementation of ECMAScript’s Property Descriptor.
  • Boa’s implementation of ECMAScript’s Realm Records
  • Boa’s implementation of ECMAScript’s Scripts.
  • A UTF-16–encoded, reference counted, immutable string.
  • Boa’s implementation of ECMAScript’s global Symbol object.
  • Boa’s ECMAScript Value implementation.
  • Boa’s ECMAScript Virtual Machine



  • This represents a ECMASCript specification [HostDefined] field.
  • A source of ECMAScript code.


  • Substitute for the Drop trait for garbage collected types.
  • A utility trait to make working with function arguments easier.
  • The Trace trait, which needs to be implemented on garbage-collected objects.

Type Aliases§

  • The result of a Javascript expression is represented like this so it can succeed (Ok) or fail (Err)

Derive Macros§