FS Module

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

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

<Buffer 68 65 6c 6c 6f 20 6e 6f 64 65>
         
    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
 

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'); 
       }
        
    })