js-sandbox

js-sandbox is a Rust library for executing JavaScript code from Rust in a secure sandbox. It is based on the Deno project and uses serde_json for serialization.

This library's primary focus is embedding JS as a scripting language into Rust. It does not provide all possible integrations between the two languages, and is not tailored to JS's biggest domain as a client/server side language of the web.

Instead, js-sandbox focuses on calling standalone JS code from Rust, and tries to remain as simple as possible in doing so. The typical use case is a core Rust application that integrates with scripts from external users, for example a plugin system or a game that runs external mods.

This library is in early development, with a basic but powerful API. The API may still evolve considerably.

Examples

Print from JavaScript

The Hello World example -- print something using JavaScript -- is one line, as it should be:

fn main() {
    js_sandbox::eval_json("console.log('Hello Rust from JS')").expect("JS runs");
}

Call a JS function

A very basic application calls a JavaScript function triple() from Rust. It passes an argument and accepts a return value, both serialized via JSON:

use js_sandbox::{Script, AnyError};

fn main() -> Result<(), AnyError> {
    let js_code = "function triple(a) { return 3 * a; }";
    let mut script = Script::from_string(js_code)?;

    let arg = 7;
    let result: i32 = script.call("triple", &arg)?;

    assert_eq!(result, 21);
    Ok(())
}

An example that serializes a JSON object (Rust -> JS) and formats a string (JS -> Rust):

use js_sandbox::{Script, AnyError};
use serde::Serialize;

#[derive(Serialize, PartialEq)]
struct Person {
    name: String,
    age: u8,
}

fn main() -> Result<(), AnyError> {
    let src = r#"
        function toString(person) {
            return "A person named " + person.name + " of age " + person.age;
        }"#;

    let mut script = Script::from_string(src)
        .expect("Initialization succeeds");

    let person = Person { name: "Roger".to_string(), age: 42 };
    let result: String = script.call("toString", &person).unwrap();

    assert_eq!(result, "A person named Roger of age 42");
    Ok(())
}

Maintain state in JavaScript

It is possible to initialize a stateful JS script, and then use functions to modify that state over time. This example appends a string in two calls, and then gets the result in a third call:

use js_sandbox::{Script, AnyError};

fn main() -> Result<(), AnyError> {
    let src = r#"
        var total = '';
        function append(str) { total += str; }
        function get()       { return total; }"#;

    let mut script = Script::from_string(src)
        .expect("Initialization succeeds");

    let _: () = script.call("append", &"hello").unwrap();
    let _: () = script.call("append", &" world").unwrap();
    let result: String = script.call("get", &()).unwrap();

    assert_eq!(result, "hello world");
    Ok(())
}