Can't write webpack loader using es6 imports

Question

I wrote this webpack loader

module.exports = function(source) {
    return `export default 'hello'`;
}

that I want to rewrite using es6 imports

export default function loader(source) {
    return `export default 'hello'`;
}

without success

SyntaxError: Unexpected token export

---

My webpack configuration is:

const path = require('path')

module.exports = {
    mode: 'development',
    entry: './src/index.js',
    output: {
        filename: 'bundle.js',
        path: path.resolve(__dirname, 'dist'),
    },,
    resolveLoader: {
        modules: [
            'node_modules',
            path.resolve(__dirname, 'loaders')
        ]
    },
    module: {
        rules: [{
            test: /\.m?js$/,
            exclude: /node_modules/,
            use: {
                loader: 'babel-loader',
                options: {
                    presets: ['@babel/preset-env']
                }
            }
        }, {
            test: /\.txt$/,
            use: {
                loader: 'my-loader'
            }
        }]
    }
};

How can I do this?