详解nodeJS中读写文件方法的区别

fs.readFile('./test.txt', 'utf8', function(err, data){
  console.log(data); 
});

var data = fs.readFileSync('./test.txt', 'utf8');
console.log(data);

//异步方法
fs.writeFile('./message.txt', '这是第一行',function(err){
  if(err) console.log('写文件操作失败');
  else console.log('写文件操作成功');
});

//同步方法
fs.writeFileSync('./message.txt','这是第一行');

var fs = require('fs');
fs.open('./message.txt','r',function(err,fd){
  var buf = new Buffer(225);
  //读取fd文件内容到buf缓存区
  fs.read(fd,buf,0,9,3,function(err,bytesRead,buffer){
    console.log(buf.slice(0,bytesRead).toString());
  }); 
  var buff = new Buffer(225);
  //位置设置为null会默认从文件当前位置读取
  fs.read(fd,buff,0,3,null,function(err,bytesRead,buffer){
    console.log(buff.slice(0,bytesRead).toString());
  });

  var buffer = new Buffer(225);
  //同步方法读取文件
  var bytesRead = fs.readFileSync(fd,buffer,0,9,3);
  console.log(bytesRead);
  console.log(buffer.slice(0,bytesRead).toString());
});

var fs = require('fs');
var buf = new Buffer('我喜爱编程');
fs.open('./mess.txt','w',function(err,fd){
  fs.write(fd,buf,3,9,0,function(err,written,buffer){
    fs.write(fd,buf,12,3,null,function(err,written,buffer){
      if(err) console.log('写文件操作失败');
      console.log('写文件操作成功');
    });
  });
  //同步写入
  fs.writeSync(fd,buf,3,9,0);
});

var fs = require('fs');
var readStream = fs.createReadStream('./message.txt',{start:3,end:12});
readStream.on('open',function(fd){
  console.log('开始读取文件');
});
readStream.on('data',function(data){
  console.log('读取到数据：');
  console.log(data);
});
readStream.on('end',function(){
  console.log('文件已全部读取完毕');
});
readStream.on('close',function(){
  console.log('文件被关闭');
});
readStream.on('error',function(err){
  console.log('读取文件失败');
});

var fs = require('fs');
var file = fs.createReadStream('./message.txt');
var out = fs.createWriteStream('./anotherMessage.txt');
file.on('data',function(data){
  out.write(data);
});
out.on('open',function(fd){
  console.log('需要被写入的文件已打开');
});
file.on('end',function(){
  //将操作系统缓存区中的数据全部写入文件
  out.end('再见',function(){
    console.log('文件全部写入完毕');
    console.log('共写入'+out.bytesWritten+'数据');
  });
});

//监听writeStream对象的drain事件
var fs = require('fs');
var out = fs.createWriteStream('./test1.txt');
for(var i=0;i<10000;i++){
  //返回true或false true代表缓存区已满
  var flag = out.write(i.toString());
  console.log(flag);
}
out.on('drain',function(){
  console.log('操作系统缓存区中的数据已全部输出');
  var out = fs.createWriteStream('./test2.txt');
  for(var i=0;i<10;i++){
    var flag = out.write(i.toString());
    console.log(flag);
  }
  out.on('drain',function(){
    console.log('操作系统缓存区中的数据已全部输出');
  });
});