babel.config.js

module.exports = function (api) {
    // Cache the returned value forever and don't call this function again.
    api.cache(true);

    // Don't cache at all. Not recommended because it will be very slow.
    //api.cache(false);

    // Cached based on the value of some function. If this function returns a value different from
    // a previously-encountered value, the plugins will re-evaluate.
    //var env = api.cache(() => process.env.NODE_ENV);

    // If testing for a specific env, we recommend specifics to avoid instantiating a plugin for
    // any possible NODE_ENV value that might come up during plugin execution.
    //var isProd = api.cache(() => process.env.NODE_ENV === "production");

    // .cache(fn) will perform a linear search though instances to find the matching plugin based
    // based on previous instantiated plugins. If you want to recreate the plugin and discard the
    // previous instance whenever something changes, you may use:
    //var isProd = api.cache.invalidate(() => process.env.NODE_ENV === "production");

    // Note, we also expose the following more-verbose versions of the above examples:
    //api.cache.forever(); // api.cache(true)
    //api.cache.never();   // api.cache(false)
    //api.cache.using(fn); // api.cache(fn)
    return {
        presets: [
            [
                '@babel/preset-env',
                Object.assign({}, process.env.NODE_ENV === 'test'
                    ? {
                        targets: {
                            node: 12,
                        }
                    }
                    : {
                        modules: false,
                        exclude: ['transform-regenerator', 'transform-async-to-generator'],
                    }
                )
            ]
        ],
        plugins: [
            ['@babel/plugin-transform-react-jsx', {
                pragma: 'h'
            }],
            '@babel/plugin-syntax-dynamic-import',
            '@babel/plugin-transform-object-assign',
            '@babel/plugin-proposal-object-rest-spread',
            ['module:fast-async', { spec: true }]
        ]
    };
};