使用Promise 读取文件，解决回调地狱问题

const fs = require('fs');


{
  let fn1 = (fpath) => {
    return new Promise((resolve, reject) => {
      fs.readFile(fpath, 'utf-8', (err, datastr) => {
        if (err) reject(err);
        resolve(datastr);
      });
    });
  };

  fn1('./11.txt')
    .then((datastr) => {
      console.log(datastr);

      return fn1('./2.txt');
    })
    .then((datastr) => {
      console.log(datastr);

      return fn1('./3.txt')
    }).then((datastr)=>{
        console.log(datastr);
        
    }).catch((err)=>{
        console.log('error message-------------- '+err.message);
        
    });
}