code: function insertEventListener (config) {
    let outFile = path.join(process.cwd(), config.outputfile);
    let tempFile = `${outFile.slice(0, outFile.lastIndexOf('.'), 0)}.temp${outFile.slice(outFile.lastIndexOf('.'))}`;
    // read in generated emscripten file
    fs.readFile(outFile, 'utf-8', (err1, data) => {
      if (err1) process.stderr.write(colors.white(err1));
      // insert eventListener
      data = data.replace(/else\{doRun\(\)\}/g, 'else{doRun()}script.dispatchEvent(doneEvent);');
      // write data to temporary file
      fs.writeFile(tempFile, data, (err2) => {
        if (err2) process.stderr.write(colors.white(err2));
        // rename temporary file to original file name
        fs.renameSync(tempFile, outFile);
      });
    });
  }
docs: Inserts an event listener into the autogenerated lib.js file
  to notify us when WebAssembly has finished loading. As of April 2017,
  this is needed because Firefox doesn't reliably emmit a script onload
  notification
  @param {Object} config