Develop and test a function locally

Run a function on your own machine with Azion CLI, send it real requests, and supply environment variables from a local file before you deploy.

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You can run a function on your own machine with Azion CLI and send it real requests before deploying. The azion dev command starts a local development server for the current project. You read the response your code returns without deploying it first.

Prerequisites

  • Azion CLI installed, and a personal token saved with azion -t <your-token>.
  • A project on your machine. To create one, run azion init and select the Javascript preset.

Run the function locally

azion dev builds the project and serves it from your machine. To start the server:

azion dev

The command builds the project first, then prints the address it is serving on:

[Azion Bundler] [Server] › ✔ success Function running on port http://localhost:3000

Use the address the command prints. To choose the port yourself, pass --port:

azion dev --port 4000

With the server running, send the function a request from another terminal:

curl http://localhost:3000/

The response your handler returns appears in the terminal. Anything the code writes with console.log() appears in the terminal running azion dev.

Provide environment variables locally

A function reads a variable with Azion.env.get(), which takes the key and returns the value:

JavaScript
01export default {
02 async fetch(request, env, ctx) {
03 const message = Azion.env.get('GREETING_MESSAGE') || 'Default value';
04
05 return new Response(message, {
06 headers: { 'content-type': 'text/plain' }
07 });
08 }
09};

The || 'Default value' fallback matters locally: Azion.env.get() returns undefined for a key that is not set. A handler that reads a variable directly into a response then returns the string undefined instead of failing. Give every variable a fallback, and the function runs before any variable exists.

Keep local values in a .env file next to the project, one KEY="value" pair per line:

GREETING_MESSAGE="Hello from your machine"

azion deploy reads .edge/.env by default. To point it at a different file, pass --env:

azion deploy --env .env

Never commit a file that holds real credentials. Keep a .env.example with the keys and placeholder values in version control, and keep the real .env out of it.

Choose where to test a function

Three surfaces run a function before it serves production traffic, and they answer different questions.

SurfaceWhere it runsReach for it when
Local developmentYour machine, through azion devYou are iterating on code, want real requests with your own headers and bodies, and want the edit-run loop to be fast
Preview deploymentAzion ConsoleYou are working in the Console and want to read the response to one simulated request, built by PreviewProvider, without leaving the editor
Code editorAzion ConsoleYou are writing or correcting the code itself and want syntax highlighting and IntelliSense

Local development is the only one of the three that accepts a request you compose yourself. It is where you exercise a handler across methods, headers, and bodies. Preview deployment sends one simulated request and renders the response.

Next steps

Deploy a function with Azion CLITake the project you just ran locally and deploy it from the terminal.Environment variablesThe fields, the caps, and the interfaces that create a variable on the account.Azion CLI devEvery flag the dev command accepts.Troubleshoot function execution and logsRead the log output of a function once it is deployed.