Fastify-cli with ES modules instead of CommonJS

Question

I'm currently switching from CommonJS modules to ES modules and encountering some issues with my Fastify-Cli project.

I'm using a custom logging module which I'm setting when running the command

fastify start -P -L ./utils/multi-stream-logger.js -o app.js

Problem is it doesn't work anymore as a ES module, error is:

Error [ERR_REQUIRE_ESM]: require() of ES Module multi-stream-logger.js from fastify-cli/util.js not supported.

Instead change the require of multi-stream-logger.js in fastify-cli/util.js to a dynamic import() which is available in all CommonJS modules.
    at requireModule (fastify-cli/util.js:29:12)
    at runFastify (fastify-cli/start.js:98:16) {
  code: 'ERR_REQUIRE_ESM'

As the require is inside the fastify-cli lib (fastify-cli/util.js) I can't change the require of the module. How can I solve this so this works with an ES module?

Answer 1

I've encountered the same problem today, loading aditional logger configuration file seems not supported in ES module projects(with type: "module" in nearest package.json) yet.

Here is how I fixed the logger customizing issue, instead of specifying an external logger configuration file, we could set FastifyServerOptions in our app.js/app.ts file.

1. If your project was automatically generated by fastify-cli with it's template, you should find the code like below in your app.js or app.ts file.

app.ts (in my ts project)

// Pass --options via CLI arguments in command to enable these options.
const options: AppOptions = {
    logger: {
        level: 'info',
        customLevels: {
            test: 99
        }
    }
}

or app.js

// Pass --options via CLI arguments in command to enable these options.
module.exports.options = {
  logger: {
     level: 'info',
}

2. Append -o flag in your fastify-cli command, eg. fastify start -o -P app.js

Wish this could help you with your logger issue.

Answer 2

So potentially this is a bug. For everyone who has the same issue, my temporary hackfix:

I simply use this one file as CommonJS module, the rest of the files in my project are ES modules now. As the ".cjs" file extension here also doesn't work, I created a new folder and put the multi-stream-logger.js in there together with a new package.json file with the following content (only this one line): { "type": "commonjs" }

That way all files in that folder are interpreted as CommonJS modules and the multi-stream-logger.js import worked, I can start with following command (mind the new cjs folder):

fastify start -P -L ./utils/cjs/multi-stream-logger.js -o app.js