Rust vs JavaScript: Key Differences Recap

Rust and JavaScript are very different languages designed for different goals. Rust focuses on safety and performance with strong typing and no garbage collector, while JavaScript prioritizes flexibility and rapid development in the browser and beyond.

If you are a JavaScript developer learning Rust, you have probably already noticed how much stricter Rust is. At first, it can feel limiting but that strictness is what gives Rust its speed and reliability. Once I started seeing Rust’s rules as guides, not roadblocks, everything started to click.

In this post, I will highlight the core differences between Rust and JavaScript, focusing on what makes Rust feel new (and sometimes confusing) for web developers.

1. Type System

• JavaScript: Dynamically typed. Types are flexible and can change at runtime.
• Rust: Statically typed. Every variable has a fixed type known at compile time.

JavaScript:

let x = 5;
x = "hello"; // allowed

Rust:

let x = 5;
x = "hello"; // type mismatch

Rust enforces this to prevent bugs early.

2. Memory Management

• JavaScript: Uses a garbage collector to clean up unused memory.
• Rust: Uses ownership and borrowing rules. No garbage collector.

This is a big shift. Rust gives you precise control over memory, but you must learn rules like ownership, borrowing, and lifetimes.

3. Variables and Mutability

• JavaScript: Variables can be reassigned by default using let.
• Rust: Variables are immutable by default. Use mut to make them mutable.

Rust:

let mut name = String::from("Alice");
name = String::from("Bob");

This helps make code more predictable.

4. Null and Undefined

• JavaScript: null and undefined are common and often cause errors.
• Rust: Uses Option for safe absence of values.

Rust forces you to handle None explicitly:

let name: Option<String> = Some("Alice".to_string());

This avoids null reference errors entirely.

5. Error Handling

• JavaScript: Uses try/catch for exceptions.
• Rust: Uses Result for recoverable errors, and panic! for unrecoverable ones.

Rust example:

fn divide(a: f64, b: f64) -> Result<f64, String> {
    if b == 0.0 {
        Err(String::from("Cannot divide by zero"))
    } else {
        Ok(a / b)
    }
}

You must handle both success and failure clearly.

6. Functions

• Both languages support first-class functions and closures.
• Rust functions have strict type signatures and return types.

Rust:

fn add(a: i32, b: i32) -> i32 {
    a + b
}

JavaScript:

function add(a, b) {
    return a + b;
}

No type guarantees in JS, strict in Rust.

7. Asynchronous Programming

• JavaScript: Built-in async/await, promises, and event loop.
• Rust: async/await is available but requires an async runtime like tokio or async-std.

Rust:

async fn fetch_data() {
    // ...
}

But to run it, you need:

#[tokio::main]
async fn main() {
    fetch_data().await;
}

It is more powerful but needs setup.

8. Tooling

• JavaScript: Uses tools like npm, ESLint, Prettier, Webpack
• Rust: Uses Cargo, clippy, rustfmt, and rust-analyzer

Rust tooling is official and consistent.

9. Compilation vs Interpretation

• JavaScript: Interpreted at runtime or JIT compiled by engines like V8.
• Rust: Compiled ahead-of-time to native machine code. No runtime needed.

This is why Rust is often used for performance-critical applications.

10. Community Libraries

• JavaScript: Massive ecosystem on npm.
• Rust: Smaller, growing ecosystem on crates.io. Focuses more on safety and quality.

Crates often work well out of the box with good documentation.

Summary Table

Final Word

Rust and JavaScript serve different goals. JavaScript prioritizes ease and speed for web development, while Rust offers safety, performance, and low-level control. If you are coming from JavaScript, expect a learning curve but also expect your code to be more predictable and reliable than ever before.