text: const fs = require('fs');
  
  let rs = fs.createReadStream('a.txt');
  // 将a.txt写到b.txt
  let ws = fs.createWriteStream('a_copy.txt');
  
  rs.pipe(ws);
  
  rs.on("error", (err) => {
      console.log(err);
  });
  
  
  ws.on("finish", () => {
      console.log("finish");
  });