Rust for JavaScript Developers: Integrating WASM in 2025

Unlock native performance in your web apps. Learn how to bridge the gap between JavaScript and Rust using WebAssembly.

📅 November 22, 2025•⏱️ 35 min read•🏷️ Systems Programming

Introduction

JavaScript is the language of the web, but sometimes it hits a performance ceiling. Heavy computations like image processing, complex algorithms, or cryptography can bog down the main thread.

Enter Rust. With its memory safety guarantees and blistering speed, it's the perfect companion to JavaScript via WebAssembly (WASM). In 2025, the tooling is mature, making it easier than ever to drop Rust modules into your Next.js apps.

💡 Why This Matters: You don't have to rewrite your whole app. You can surgically replace performance bottlenecks with Rust.

Key Concepts

Setting Up Rust for WASM

We'll create a simple Rust function to calculate the Fibonacci sequence recursively—a classic CPU-bound task.

src/lib.rs

use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn fibonacci(n: u32) -> u32 {
    match n {
        0 => 0,
        1 => 1,
        _ => fibonacci(n - 1) + fibonacci(n - 2),
    }
}

#[wasm_bindgen]
pub fn greet(name: &str) -> String {
    format!("Hello, {}! This is Rust talking.", name)
}

Build this with wasm-pack build --target web to generate the necessary glue code.

Integration with Next.js

Now, let's load this WASM module in a Next.js component. We'll use dynamic imports to load the module asynchronously.

components/RustCalculator.tsx

'use client';
import { useEffect, useState } from 'react';
import init, { fibonacci } from '@/pkg/my_rust_lib';

export default function RustCalculator() {
  const [result, setResult] = useState<number | null>(null);
  const [isReady, setIsReady] = useState(false);

  useEffect(() => {
    init().then(() => setIsReady(true));
  }, []);

  const calculate = () => {
    if (!isReady) return;
    const start = performance.now();
    const res = fibonacci(40);
    const end = performance.now();
    console.log(`Calculation took ${end - start}ms`);
    setResult(res);
  };

  return (
    <div>
      <button
        onClick={calculate}
        disabled={!isReady}
        className="bg-orange-600 text-white px-4 py-2 rounded"
      >
        Calculate Fib(40) in Rust
      </button>
      {result && <p>Result: {result}</p>}
    </div>
  );
}

Rust vs Spring Boot

It's important to know when to use what. While Rust via WASM is great for client-side compute, Spring Boot remains the king of enterprise backend services.

Rust (WASM)

Runs in the browser (Client-side)
Zero latency (no network call)
Best for image editing, crypto, compression
Offloads work from the server

Spring Boot (Java)

Runs on the server (Backend)
Access to databases and private APIs
Best for complex business logic, transactions
Secure environment for sensitive data

Spring Boot Controller (The Traditional Way)

@GetMapping("/fibonacci/{n}")
public int getFibonacci(@PathVariable int n) {
    // This runs on the server, adding latency for the network round trip
    return fibService.calculate(n);
}

Security Considerations

WASM is sandboxed, but that doesn't mean it's invulnerable.

🔒 Sandboxing

WASM cannot access the DOM or network directly; it must go through JS glue code.

🔒 Memory Safety

Rust prevents buffer overflows, a common vulnerability in C/C++ WASM modules.

🔒 Supply Chain

Audit your Rust crates just like you audit npm packages.

🔒 Side Channels

Be aware of timing attacks if performing crypto operations in WASM.

✅ Rust Integration Checklist

Ready to deploy your first WASM module?

Measure Performance

Compare your new WASM modules against standard JS. Use our tools to visualize the difference.

Explore Tools →Read More Blogs

Conclusion

Rust and WASM are not here to replace JavaScript, but to augment it. By identifying the CPU-intensive parts of your application and moving them to Rust, you can achieve performance gains that were previously impossible in the browser.

Start small. Pick one function, one algorithm, and rewrite it in Rust. The results will speak for themselves.