let fs = require('fs');
 
fs.readFile('./a.txt',(err,data)=>{
    if(err){
        console.log(err);
    }else{
        console.log(data.toString());
    }
})
 
fs.writeFile('b.txt','月薪2元',{flag:"a"},(err)=>{
 if(err){
     throw err
 }
})