code: async function build( inputOpts, outputOpts ) {
  
    // create a bundle
    const bundle = await rollup.rollup( inputOpts );
  
    // generate code and a sourcemap
    const { code, map } = await bundle.generate( outputOpts );
  
    console.log( 'Writing file: ' + outputOpts.file );
    writeFile( outputOpts.file, code );
  
    console.log( 'Generated bundle: ', bundle.getTimings()[ '# GENERATE' ] );
  
  }
docs: stderr to stderr to keep `rollup main.js > bundle.js` from breaking const stderr = console.error.bind( console );