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The FastEdge JavaScript SDK (@gcoredev/fastedge-sdk-js) compiles JavaScript applications to WebAssembly so they can run on Gcore’s edge network. It is the recommended way to build FastEdge applications in JavaScript. Node.js v22 or higher is required.

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Install the SDK

The steps below set up a minimal project manually. To scaffold a project from a template instead, run npm create fastedge-app — it handles folder creation, dependency installation, and project structure interactively. 
mkdir my-app
cd my-app
npm init -y
npm install --save-dev @gcoredev/fastedge-sdk-js
npm init -y creates package.json with "type": "commonjs" by default. The SDK bundler requires ESM — change it before building: 
npm pkg set type=module
After installation, three CLI tools are available via npx:
ToolPurpose
fastedge-buildCompiles JavaScript to a WebAssembly binary
fastedge-initCreates build config for repeatable builds
fastedge-assetsPackages static files for edge serving

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Write a handler

FastEdge applications register a fetch event listener that receives an HTTP request and returns a response. Create src/index.js: 
addEventListener('fetch', (event) => {
  event.respondWith(new Response('Hello from FastEdge'));
});
The fetch event model follows the Service Worker API convention. event.respondWith() accepts a Response object or a Promise<Response>. Under the hood, the SDK compiles to the WASI P2 wasi:http/proxy world — the same standard used by the Modern Rust SDK.

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Verify the toolchain

Compile the handler to a WebAssembly binary: 
npx fastedge-build --input src/index.js --output wasm/app.wasm
A successful build prints: 
Build success!!
"src/index.js" -> "wasm/app.wasm"
The compiled binary is at ./wasm/app.wasm. That file can be uploaded to FastEdge directly or used as the starting point for the next tutorial.