code: function copyFile(source, target, copyCallback) {
      const readStream = fs.createReadStream(source);
      const writeStream = fs.createWriteStream(target);
      let done = false;
  
      readStream.on('error', copyDone);
      writeStream.on('error', copyDone);
  
      writeStream.on('close', function onWriteCb() {
          copyDone(null);
      });
  
      readStream.pipe(writeStream);
  
      /**
       * Finish copying. Reports error when needed
       * @param [error] optional error
       */
      function copyDone(error) {
          if (!done) {
              done = true;
              copyCallback(error);
          }
      }
  }
docs: Copy a file to its new destination
  @param {string} source
  @param {string} target
  @param {function} copyCallback