Ever wondered how JavaScript runtimes like Node.js or Deno are built? Or maybe you've thought about creating your own JavaScript runtime with custom features and performance tweaks? If so, you're in the right place! In this tutorial, we'll dive into building a JavaScript runtime using Rust and the andromeda_runtime crate.
Introduction
Rust is a systems programming language that guarantees memory safety without the need for a garbage collector, making it an excellent choice for high-performance applications. By leveraging Rust's capabilities along with the andromeda_runtime crate, we can create a custom JavaScript runtime that's both fast and secure.
The andromeda_runtime crate provides a solid foundation for executing JavaScript code. It comes with recommended extensions, built-in functions, and an event loop handler, all of which simplify the process of setting up a runtime.
Prerequisites
Before we get started, make sure you have the following:
- Rust: Ensure you have Rust installed. If not, you can download it from rust-lang.org.
- Cargo: Cargo is Rust's package manager and comes bundled with Rust installations.
- Basic Knowledge of Rust: Familiarity with Rust's syntax and concepts will be helpful.
- JavaScript/TypeScript: A basic understanding of JavaScript or TypeScript.
Setting Up the Project
Let's kick things off by creating a new Rust project:
cargo new jsruntime
cd jsruntime
Next, open Cargo.toml and add the necessary dependencies:
[dependencies]
andromeda_core = { git = "https://github.com/tryandromeda/andromeda" }
andromeda_runtime = { git = "https://github.com/tryandromeda/andromeda" }
clap = { version = "4.5.16", features = ["derive"] }
tokio = { version = "1.39.0", features = ["rt", "sync", "time"] }
1. Importing Dependencies
First, we'll import the necessary crates and modules:
use andromeda_core::{Runtime, RuntimeConfig};
use andromeda_runtime::{
recommended_builtins, recommended_eventloop_handler, recommended_extensions,
};
use clap::{Parser as ClapParser, Subcommand};
Here's what each of these imports does:
-
andromeda_core: Contains the core components for building our runtime. -
andromeda_runtime: Provides recommended built-ins, extensions, and the event loop handler we'll use. -
clap: A crate for parsing command-line arguments, which we'll use to build our CLI.
2. Defining the Command-Line Interface
Next, let's define a CLI using clap:
#[derive(Debug, ClapParser)]
#[command(name = "jsruntime")]
#[command(
about = "JavaScript Runtime built for a blog post",
long_about = "JS/TS Runtime in Rust powered by Nova built for a blog post"
)]
struct Cli {
#[command(subcommand)]
command: Command,
}
#[derive(Debug, Subcommand)]
enum Command {
/// Runs a file or files
Run {
#[arg(short, long)]
verbose: bool,
#[arg(short, long)]
no_strict: bool,
/// The files to run
#[arg(required = true)]
paths: Vec<String>,
},
}
Here's what's happening:
-
CliStruct: This struct represents our command-line interface, including any subcommands and arguments. -
CommandEnum: This enum defines the available subcommands—in this case, onlyRun.
3. The Main Function
Our main function orchestrates the runtime execution:
fn main() -> Result<(), Box<dyn std::error::Error>> {
let args = Cli::parse();
let rt = tokio::runtime::Builder::new_current_thread()
.enable_time()
.build()
.unwrap();
// Run the JSRuntime in a secondary blocking thread so tokio tasks can still run
let runtime_thread = rt.spawn_blocking(|| match args.command {
Command::Run {
verbose,
no_strict,
paths,
} => {
let mut runtime = Runtime::new(RuntimeConfig {
no_strict,
paths,
verbose,
extensions: recommended_extensions(),
builtins: recommended_builtins(),
eventloop_handler: recommended_eventloop_handler,
});
let runtime_result = runtime.run();
match runtime_result {
Ok(result) => {
if verbose {
println!("{:?}", result);
}
}
Err(error) => runtime.agent.run_in_realm(&runtime.realm_root, |agent| {
eprintln!(
"Uncaught exception: {}",
error.value().string_repr(agent).as_str(agent)
);
std::process::exit(1);
}),
}
}
});
rt.block_on(runtime_thread)
.expect("An error occurred while running the JS runtime.");
Ok(())
}
Let's break down what's happening in this function:
a. Parsing Arguments
We start by parsing the command-line arguments using clap:
let args = Cli::parse();
b. Setting Up the Tokio Runtime
We create a new Tokio runtime. Tokio is an asynchronous runtime for Rust that allows us to handle asynchronous operations efficiently.
let rt = tokio::runtime::Builder::new_current_thread()
.enable_time()
.build()
.unwrap();
c. Spawning a Blocking Task
We spawn a blocking task to run our JavaScript code. This ensures our runtime doesn't block other asynchronous tasks.
let runtime_thread = rt.spawn_blocking(|| match args.command { /* ... */ });
d. Handling the Run Command
Within the spawned task, we match the command:
Command::Run {
verbose,
no_strict,
paths,
} => {
let mut runtime = Runtime::new(RuntimeConfig { /* ... */ });
let runtime_result = runtime.run();
match runtime_result {
Ok(result) => { /* ... */ }
Err(error) => { /* ... */ }
}
}
Here's what's going on:
-
Creating the Runtime: We instantiate a new
Runtimewith the provided configuration. -
Running the Runtime: We call
runtime.run()to execute the JavaScript code. -
Handling Results: If the execution is successful, we print the result if
verboseis enabled. If there's an error, we print the uncaught exception.
e. Blocking on the Runtime Thread
Finally, we wait for the spawned task to complete:
rt.block_on(runtime_thread)
.expect("An error occurred while running the JS runtime.");
Customizing the Runtime
One of the great benefits of building your own runtime is the ability to customize it to your needs. Let's explore some ways you can tailor the runtime.
1. Adding Custom Extensions
Extensions add extra functionality to the runtime. You can add your own custom extensions or modify existing ones.
let custom_extensions = vec![
// Your custom extensions here
];
let mut runtime = Runtime::new(RuntimeConfig {
// ...
extensions: custom_extensions,
// ...
});
2. Modifying Built-ins
Built-in functions are essential for interacting with the runtime environment. You can add or customize built-in functions to suit your requirements.
let custom_builtins = vec![
// Your custom built-in functions here
];
let mut runtime = Runtime::new(RuntimeConfig {
// ...
builtins: custom_builtins,
// ...
});
3. Custom Event Loop Handler
If you need custom event loop behavior, you can provide your own event loop handler.
fn custom_eventloop_handler() {
// Your custom event loop logic here
}
let mut runtime = Runtime::new(RuntimeConfig {
// ...
eventloop_handler: custom_eventloop_handler,
// ...
});
Running the Runtime
To test your runtime, let's create a simple JavaScript file, test.js:
console.log("Hello from the JS Runtime!");
Then, run the runtime using:
cargo run run test.js
If everything is set up correctly, you should see:
Hello from the JS Runtime!
Conclusion
And there you have it! You've built a simple JavaScript runtime using Rust. Not only have you demystified how runtimes like Node.js and Deno work, but you've also set the foundation for endless possibilities in customizing and extending your own runtime.
Remember, this is just the beginning. Keep experimenting, add new features, and most importantly, have fun along the way!
Happy coding! 🚀
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