mix() {
        const path = this.root(
            process.env && process.env.MIX_FILE ? process.env.MIX_FILE : 'webpack.mix'
        );

        try {
            require.resolve(`${path}.cjs`);

            return `${path}.cjs`;
        } catch (err) {
            //
        }

        return path;
    }
Determine the path to the user's webpack.mix.js file.