wasm-pack - Rust to WebAssembly Without the Build Hell

wasm-pack is a Rust CLI tool that's supposed to make compiling Rust to WebAssembly easy. The good news: it usually works. The bad news: when it doesn't work, you'll spend hours figuring out why your perfectly fine Rust code won't compile to WASM.

Originally built by the Rust and WebAssembly Working Group, which got archived in August 2025 with zero warning, leaving maintainers scrambling to figure out what the hell happened. Now it's maintained by @drager, who took over when rustwasm went dark.

The tool handles the tedious parts: generating JavaScript bindings, optimizing WASM binaries, and creating npm packages. Without it, you'd be manually configuring wasm-bindgen, fighting with wasm-opt, and probably giving up.

How It Actually Works (When It Works)

wasm-pack wraps a bunch of other tools and prays they all work together. It runs cargo build to compile your Rust, uses wasm-bindgen to generate JavaScript glue code, optimizes everything with wasm-opt, and spits out an npm package.

The wasm-pack build command is what you'll use 99% of the time. It creates a pkg/ directory with:

• A .wasm file (hopefully smaller than 10MB)
• JavaScript bindings that somehow work
• TypeScript definitions (wrong about half the time)
• A package.json you can actually publish

When everything lines up, it's beautiful. When it goes wrong, you get cryptic bullshit like "could not compile wasm-bindgen-cli" that sends you down a 3-hour rabbit hole checking versions and clearing cache dirs.

Current Status: Barely Maintained

As of August 2025, we're on version 0.13.1 from October 2024. That's right - no releases for almost a year. The tool requires Rust 1.30.0+ (which is ancient by Rust standards).

The docs are mostly broken since the rustwasm shutdown. The official book returns 404s, so good luck finding help. You're basically on your own with Stack Overflow and GitHub issues.

Performance Reality Check

Let's be honest about performance:

• "Optimization" usually means your 100-line Rust function becomes a 2MB WASM file
• Bundle sizes are massive compared to equivalent JavaScript
• Startup time includes loading and instantiating WASM, which isn't free
• The generated bindings add overhead for every function call

wasm-opt helps, but don't expect miracles. Your "optimized" hello world will still be larger than most JavaScript libraries. Use wee_alloc if you want to shave off a few KB.

Integration Hell

Getting wasm-pack output to work with modern JavaScript tooling is... interesting.

Webpack: Requires specific configuration and experimental features. Hot reloading? Forget about it.

Vite: Works better with vite-plugin-wasm-pack, but you'll still fight with import paths.

Node.js: Use --target nodejs and pray your dependencies don't break.

The generated TypeScript types are usually wrong, so you'll end up using any everywhere or writing your own declarations.

When wasm-pack Screws You

Common ways this thing breaks:

1. Build failures: "could not compile wasm-bindgen-cli" means your versions are mismatched. Delete everything and start over.

2. Target issues: Forgot to install wasm32-unknown-unknown? You're getting cryptic errors.

3. Proxy problems: Corporate networks will break the installer. Download binaries manually.

4. Version hell: Your local wasm-bindgen version doesn't match the crate version. Welcome to dependency hell.

5. Platform differences: Works on Linux, breaks on Windows, acts weird on macOS. Classic Rust ecosystem behavior.

The tool assumes everything is configured perfectly. When it's not, you're on your own.

Despite all the warnings above, if you're still determined to use wasm-pack, here's how to get it working.

Prerequisites That'll Break

You need Rust 1.30.0+ but honestly, use something recent or you'll get weird errors. Check the Rust release history to see what's current. Install the WASM target before you forget:

rustup target add wasm32-unknown-unknown

If this fails, you're probably behind a corporate firewall. Good luck with that.

Install wasm-pack. The "official installer" link is broken since the docs died, so use cargo:

## This will probably work
cargo install wasm-pack

## If you're feeling risky (installer might be dead)
curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh

On Windows, this will randomly fail. On macOS, it might work. On Linux, it'll probably work unless you have an ARM processor.

Your First WASM Project (That Won't Work)

Don't use wasm-pack new - the templates are often broken. Instead, clone an existing project:

git clone https://github.com/rustwasm/wasm-pack-template.git my-wasm-project
cd my-wasm-project

Your `Cargo.toml` needs this or nothing will work:

[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = "0.2"

The basic src/lib.rs:

use wasm_bindgen::prelude::*;

[#[wasm_bindgen]](https://docs.rs/wasm-bindgen/latest/wasm_bindgen/attr.wasm_bindgen.html)
pub fn greet(name: &str) {
    [web_sys::console::log_1](https://docs.rs/web-sys/latest/web_sys/console/fn.log_1.html)(&format!("Hello, {}!", name).into());
}

Building (When It Actually Works)

wasm-pack build --target web

This will probably fail the first two times with version issues, then randomly work on the third try and produce a massive bundle.

If it fails:

• Delete target/ and pkg/ directories
• Run cargo clean
• Clear cargo cache with rm -rf ~/.cargo/registry
• Try again and hope for better luck

Integration Nightmare

The generated code is supposed to work with JavaScript bundlers. Reality is messier.

Webpack: You need experimental WASM support and probably custom loaders. Your webpack.config.js becomes a 200-line monster.

Vite: Better, but you still need plugins and specific import syntax.

Plain JavaScript: Actually works sometimes, which is shocking.

Example that might work:

import init, { greet } from './pkg/my_wasm_project.js';

async function run() {
    // This can fail silently
    await init();
    
    // This might work
    greet('WebAssembly');
}

run().catch(console.error);

Publishing (Good Luck)

wasm-pack build --release
wasm-pack publish

The generated package.json is usually wrong. You'll need to manually fix:

• The module paths
• The TypeScript definitions
• The dependencies

Most people just give up and copy the files manually.

Debugging Your Broken Build

When (not if) it breaks:

1. Check your Rust version: Ancient versions have weird WASM bugs
2. Clear everything: cargo clean && rm -rf pkg/
3. Check your network: Corporate proxies break everything
4. Pray to different gods: Sometimes it just starts working

Set `RUST_LOG=debug` to get more useless error messages:

RUST_LOG=debug wasm-pack build

The logs will tell you exactly what's wrong in the most cryptic way possible.