Detailed explanation of examples of reading and writing files based on the fs core module based on node.js

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The fs module in node.js

Commonly used functions

Implement the operation of reading and writing files#- Synchronization and asynchronous coexist, no need to synchronize if there is asynchronous

- fs.readFile cannot read files larger than the running memory , if the file is too large, the readFile method will not be used

- Large file split reading, stream

- let fs =require('fs')

Read files synchronously##-fs.readFileSync

let result=fs.readFileSync('./1.txt','utf8');

- fs.readFile

fs.readFile('./name.txt','utf8',function( err,data){if(err){

}else{
console.log(data)
}
})

- fs.writeFileSync

fs.writeFileSync("./1.txt",JSON.stringify({name:1}))

- fs.writeFile

fs.writeFile('./1.txt','aaaaa', function ( err) {if(err){

}
})


Read and write files and write a copy instance

let fs=require("fs");
//同步拷贝
function copySync(source,target){
//同步读取
let result=fs.readFileSync(source,'utf8');
//同步写入
fs.writeFileSync(target,result);
}
copySync("./age.txt",'./1.txt');

//Asynchronous copy

function copy(sourse,target,callback){
//异步读取
fs.readFile(sourse,'utf8',function(err,data){
if(err){
return callback(err)
}else{
//异步写入
fs.writeFile(target,data,callback)
}
});
};
copy('./name.txt','./ss.txt',function(err){
if(err) return console.log(err);
console.log('拷贝成功')
})

- fs.existsSync

stat method

stat.isDirectory to see if it is a folder

})

if(fs.existsSync('./b')){
fs.stat('./b',function (err,stat) {
//stat中的time是用来做服务器缓存
//stat.isDirectory看是不是文件夹 stat.isFile看是不是文件
if(stat.isDirectory()){
//删除文件夹
fs.rmdir('./b',function(){})
}else{
//删除文件
fs.unlink('./b',function(){});
}
})
}

Use recursion to write a folder and create it in sequence

function md(url) {
  let paths=url.split('/'); //将a/b/c拆分成数组['a','b','c']
  let index=0;
  function make(path){
    if(index===paths.length+1){ // 如果到终点，停止递归
      return false;
    }
    if(!fs.existsSync(path)){ //不存在
      //创建文件夹
      fs.mkdir(path,function () {
        make(paths.slice(0,++index).join('/'))
      })
    }else{ //存在
      make(paths.slice(0,++index).join('/'))
    }
  }
  make(paths[index++]) //先取出第一个
}
md('a/b/c/d');

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