Node JS fs Module | File System in Node JS

fs modules
read file
check file stats
write file
append file
delete file

FS Module

fs module is a build-in module in node js used to access filesystem. fs module has methods to read, write, append, rename, and delete data from a file stored in File System.

fs Module example

         
   
    const http=require('fs');

Read File

To read file in node js, we have both synchronous and asynchronous functions. We can use any one of them as per requirement.

Read File Sync Buffer

         
    const fs=require('fs');
    var data=readFileSync("data.txt");
    console.log(data);

/*data.txt*/


    hello node

The default output is in buffer. To convert to string, use toString() method.

Read File Sync

fs.readFileSync method read a file synchronously.

hello node

         
    const fs=require('fs');
    var data=readFileSync("data.txt").toString();
    console.log(data);

/*data.txt*/


    hello node

Read File

fs.readFile read any file asynchronously using a callback function as parameter. This is recommended way to read file.

hello node

         
    const fs=require('fs');
    fs.readFile("data.txt",(err,data)=>{
    if(err){
        console.log("Error : ", err);
    }
    else{
        console.log(data.toString());
    }
})

/*data.txt*/


    hello node

Read File with encoding

fs.readFile can have a option {encoding:'utf8'} to encode binary file. Without encoding, NodeJS will not decode the file into a string.

hello node

         
    const fs=require('fs');
    fs.readFile("data.txt",{encoding:'utf8'},(err,data)=>{
    if(err){
        console.log("Error : ", err);
    }
    else{
        console.log(data);  // .toString() not required
    }
})

/*data.txt*/


    hello node

Check File Stats

To check file properties in NodeJS, we use fs.stat method. Node JS provides two APIs for both synchronous and asynchronous operations.

stat method


const fs=require('fs');

fs.stat('src/data.txt', (err, stats) => {
    if (err) {
      console.error(err)
    }
    else{
        console.log(stats.isFile());      // true
        console.log(stats.isDirectory());      // false
        console.log(stats.size);      // 1024
    }
  });

statSync method


    const fs=require('fs');
            
   try{
    const stats = fs.statSync('/Users/joe/test.txt');
   }
   catch(err){
       console.error(err);
   }

Write File

To write in a file, node js use writeFile / writeFileSync methods.

    
          
    const fs=require('fs');
    fs.writeFileSync('data.txt','Hello Node');

If data.txt file is missing in current directory, node js will create a new directory with same name and then write. There is no need to create a file first and then write.

writeFileSync

To write in a file synchronously, node js used fs.writeFileSync method. The first parameter is file name and second is text data.

   
    const fs=require("fs");
    fs.writeFileSync('data.txt','Hello Node JS');

writeFile

To write in a file asynchronously, node js used fs.writeFile method. The first parameter is file name and second is text data and third is callback to handle errors..

   
    const fs=require("fs");
    fs.writeFile('data.txt',"hello Node",(err)=>{
        if(err){
            console.log(err)
        }
    })

Write File with utf-8

   
    const fs=require("fs");
    fs.writeFile('data.txt',"hello Node",'utf8',(err)=>{
        if(err){
            console.log(err)
        }
    })

Append in file

To append in a file, use appendFile or appendFileSync methods of fs. This will not overwrite in file like writeFile and writeFileSync.

appendFileSync

appendFileSync method of fs append file asynchronously.

Hello Node 1

Hello Node 2

   
const fs=require('fs');

fs.appendFileSync('src/data.txt',"hello Node 1",'utf8',(err)=>{
    if(err){
        console.log(err)
    }
});

fs.appendFileSync('src/data.txt',"hello Node 2",'utf8',(err)=>{
    if(err){
        console.log(err)
    }
});

appendFile

appendFile method of fs append file synchronously.

Hello Node 1

Hello Node 2

   
const fs=require('fs');

fs.appendFile('src/data.txt',"hello Node 1",'utf8',(err)=>{
    if(err){
        console.log(err)
    }
});

fs.appendFile('src/data.txt',"hello Node 2",'utf8',(err)=>{
    if(err){
        console.log(err)
    }
});

delete file

To delete files, node js use fs.unlink or fs.unlinkSync methods.

fs.unlinkSync

       
    const fs=require('fs');
    fs.unlinkSync('data.txt');

By using fs.unlinkSync without exception handling can create runtime errors. To handle tis, use fs.unlinkSync with exception handling

fs.unlinkSync with exception handling

       
    const fs=require('fs');
    try{
        fs.unlinkSync('data.txt');
        console.log('file deleted successfully');
    }
    catch(err){
        console.log("Error",err);
    }

fs.unlink

fs.unlink is a asynchronously method to delete file with two arguments. First is file name and second is callback function.

       
    const fs=require('fs');
    fs.unlink('data.txt',(err)=>{
       if(err){
           console.log('Error:', err);
       }
       else{
          console.log('file deleted successfully'); 
       }
        
    })