Crate js_sandbox[][src]

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.


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 ="triple", &arg)?;

	assert_eq!(result, 21);

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 " + + " 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 ="toString", &person).unwrap();

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

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

	assert_eq!(result, "hello world");



Represents a single JavaScript file that can be executed.



Evaluates a standalone Javascript expression, and returns the result as a JSON value.

Type Definitions


Polymorphic error type able to represent different error domains.


Represents a value passed to or from JavaScript.