# Azion Runtime quickstart This guide takes you through your first function on Azion Runtime, from the code to a request on the deployed domain. - Create a JavaScript function project with the Azion CLI. - Write the handler in the recommended ES Modules shape, `export default { fetch(request, env, ctx) }`. - Call a Web API and read the request metadata, an Azion API. - Run the function with `azion dev`, then deploy it and compare the two answers. The function returns four values as JSON. `EdgeRuntime` names where the code runs, `URL` and `crypto.randomUUID()` are [Web APIs](/en/documentation/devtools/runtime/api-reference/javascript/), and `request.metadata` holds the [request metadata](/en/documentation/devtools/runtime/api-reference/metadata/) that Azion adds to every request. --- ## Prerequisites - The Azion CLI, installed and logged in. For the setup, refer to [Azion CLI quickstart](/en/documentation/devtools/cli/quickstart/). - Node.js and npm. The CLI runs the Azion bundler with `npx` to build the project. - `curl` on your machine. --- ## Create the project Create a project named `my-runtime-function` with the CLI: ```bash azion init --name my-runtime-function ``` The command asks five questions. Select the *Javascript* preset and the *Hello World* template, enter `Y` to install the dependencies, and enter `n` to the local server and to the deploy. You run both after you write the handler. The command confirms the project: ```text Your application my-runtime-function was initialized successfully ``` The function entry is `index.js`, at the root of the new `my-runtime-function` directory. The template writes it in the older `export default main` shape, which the build reports as deprecated. For every shape the runtime accepts, refer to [Handlers](/en/documentation/devtools/runtime/api-reference/handlers/). --- ## Write the handler Replace the contents of `index.js` with this handler: ```javascript export default { async fetch(request, env, ctx) { const url = new URL(request.url); return Response.json({ runtime: EdgeRuntime, path: url.pathname, requestId: crypto.randomUUID(), country: request.metadata?.geoip_country_name ?? null, }); }, }; ``` The runtime calls `fetch` once per request: - `request` is the incoming [Request](/en/documentation/devtools/runtime/api-reference/request/), and `request.metadata` carries the GeoIP and network data of the request. - `env` holds the environment variables, and `ctx` carries `waitUntil()`. This handler uses neither. - `Response.json()` builds a [Response](/en/documentation/devtools/runtime/api-reference/response/) with the object as a JSON body and `content-type: application/json`. The optional chaining in `request.metadata?.` keeps the handler working under `azion dev`, where the request carries no metadata. --- ## Run the function locally Go to the project directory and start the local development server: ```bash cd my-runtime-function azion dev ``` The command builds the function and serves it on port 3333: ```text [Azion] [Build] › ℹ info Using preset: javascript [Azion] [Pre-Build] › ℹ info Starting pre-build... [Azion] [Pre-Build] › ℹ info Pre-build completed successfully [Azion] [Build] › ℹ info Using preset default entry: index.js [Azion] [Build] › ℹ info Starting build... [Azion] [Build] › ✔ success Build completed successfully [Azion] [Post-Build] › ℹ info Starting post-build... [Azion] [Post-Build] › ✔ success Post-build completed successfully [Azion] [Server] › ✔ success Function running on port 0.0.0.0:3333, url: http://localhost:3333 [Azion] [Server] › ℹ info Initial scan complete. Ready for changes. ``` The build prints no deprecation warning, because the handler uses the ES Modules shape. In a second terminal, request a path: ```bash curl -s -i 'http://localhost:3333/hello' ``` The function answers with JSON: ```text HTTP/1.1 200 OK content-type: application/json Date: Thu, 01 Jan 2026 12:00:00 GMT Connection: keep-alive Keep-Alive: timeout=5 Transfer-Encoding: chunked {"runtime":"edge-runtime","path":"/hello","requestId":"9b2138b1-02f0-433c-aee5-9442142996b2","country":null} ``` Locally, `EdgeRuntime` is `edge-runtime` and `country` is `null`, because `azion dev` adds no request metadata. To stop the server, press `Ctrl+C`. For everything that differs between `azion dev` and a deployed function, refer to [How Azion Runtime works](/en/documentation/devtools/runtime/how-it-works/#local-and-deployed-behavior). --- ## Deploy the function From the `my-runtime-function` directory, deploy the project: ```bash azion deploy ``` The command uploads the project, builds it, creates the function, the application, and the workload, and prints the domain of the workload: ```text Running deploy command Uploading source files Upload completed successfully! … Your Application was deployed successfully To visualize your application access the Domain: https:// Your application is being deployed to all Azion Locations and it might take a few minutes. ``` The first deploy can take several minutes to answer from every location. Until a location has the function, it answers `404` with a page titled `There's nothing here yet`. Wait and retry before you diagnose the deploy. --- ## Request the deployed function Request the same path from the domain that `azion deploy` printed. Replace `` with that domain: ```bash curl -s -i 'https:///hello' ``` The deployed function answers with the same keys: ```text HTTP/2 200 date: Thu, 01 Jan 2026 12:00:00 GMT content-type: application/json x-azion-request-id: 0123456789abcdef0123456789abcdef x-azion-edge-location: alt-svc: h3=":443"; ma=86400 {"runtime":"azion","path":"/hello","requestId":"1aa1a614-a0ca-4291-93a1-66fa1c57ebc9","country":"Brazil"} ``` Deployed, `EdgeRuntime` is `azion`, and `country` holds the country of the client that sent the request, from the request metadata. `requestId` changes on every request. The function runs on Azion Runtime and answers on the workload domain. To change the function, edit `index.js` and run `azion deploy` again from the `my-runtime-function` directory. Later deploys take about two minutes to answer from every location. --- ## Next steps - [How Azion Runtime works](/en/documentation/devtools/runtime/how-it-works.md): The execution model, the handler shapes, the bundler, and what differs under azion dev. - [Web APIs](/en/documentation/devtools/runtime/api-reference/javascript.md): Every Web API the runtime provides, from fetch and streams to Web Crypto. - [Node.js APIs](/en/documentation/devtools/runtime/node.md): The Node.js modules the build resolves, and how each one behaves when deployed. - [Functions quickstart](/en/documentation/platform/functions/quickstart.md): Create a function in Azion Console and run it on an application.