The Functions Framework >= 1.9.0 supports loading your code as an ES Module.

ECMAScript modules (ES modules or ESM) are a TC39 standard, unflagged feature in Node >=14 for loading JavaScript modules. As opposed to CommonJS, ESM provides an asynchronous API for loading modules and provides a very commonly adopted syntax improvement via import and export statements.

Before:

exports.helloGET = (req, res) => {
 res.send('No ESM.');
};

After:

export const helloGET = (req, res) => {
 res.send('ESM!');
};

Create a package.json file:

{
  "type": "module",
  "scripts": {
    "start": "functions-framework --target=helloGET"
  },
  "main": "index.js",
  "dependencies": {
    "@google-cloud/functions-framework": "^1.9.0"
  }
}

Create a index.js file:

export const helloGET = (req, res) => {
  res.send('ESM!');
};

Install dependencies and start the framework:

npm i
npm start

Go to localhost:8080/ and see your function execute!