AutoStash

WASM-powered browser extension in Rust that saves form progress into chrome storage, so you don't have to refill the online forms if the submit button failed or browser crashed. Icon generatd with Google Gemini.

Tools You’ll Use:

• wasm-bindgen: for JS interop
• wasm-pack: to compile Rust to WebAssembly
• JavaScript wrapper to load the WASM module in your extension

Test with Chrome Extension Developer mode

Build the wasm module

wasm-pack build --target web

Navigate to Chrome extensions, turn on Developer mode and load the module unpacked.

Why this is a Rust library and not an executable

Rust project for your browser extension is a library (lib) instead of an executable (bin) has to do with how WebAssembly integrates into the browser.

When you compile Rust to WebAssembly for the web, you're not running a standalone binary (like you would with a CLI app). Instead:

• The browser loads your .wasm file like a module.

• JavaScript acts as the “main” runner.

• Your Rust code exposes functions using #[wasm_bindgen] so JS can call them.

• The Rust function #[wasm_bindgen(start)] acts like the “main” entry point, but this optional. It’s just a convenient hook for running initialization logic automatically when the WASM module is loaded (by calling the init() function in JavaScript which is automatically generated by wasm-pack.). You don’t need it if you're exporting functions and calling them from JS. Many extensions/modules avoid it to keep JS in full control of lifecycle.

So your crate needs to be a cdylib:

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

This tells Rust to compile into a shared binary format that other languages (JS, in this case) can load, so it can interop with JS, be used in browser extensions, and works in browsers.

Rust executables ([[bin]]) compile to native machine code — not WebAssembly. Even if you tried to use main.rs and fn main(), it wouldn’t work in a browser because:

• Browsers don’t know how to run a native Rust binary.

• There's no terminal/CLI to invoke it.

• You need to interoperate with the DOM, events, etc., which requires JS integration.