The tutorial provides the detail about the node.js file processing mechanism and how to use the node.js fs module. The node.js fs module provides the I/O operations modeled around standard POSIX functions. The fs module can be accessed using the below command:

const fs = require('fs');

synchronous and asynchronous form in the node.js file system

The node.js fs module provides the support for synchronous and asynchronous forms. The exceptions occured in the synchronous forms are thrown immediately using the try…catch { } . The Asynchronous forms provides arguments where last arguments always returns the callback. The first arguments is available for capturing the exception. If there is no exception then first argument will be returned as null /undefined.

Place the file at the location and mention it in the sample program for asynchronous form execution

const fs = require('fs');
fs.unlink('/tmp/test-fs-async/remove-async-file.txt', (err) => {
  if (err) throw err;
  console.log('The file removed successfully from the path -/tmp/test-fs-async/remove-async-file.txt');
});

C:\Users\user\Desktop >node fs-async.js
The file removed succesfully from the path -tmp/test-fs-async/remove-async-file.txt

sample program for the synchronous form execution

const fs = require('fs');
try {
  fs.unlinkSync('/tmp/test-fs-async/remove-async-file.txt');
   console.log('The file removed successfully from the path -/tmp/test-fs-async/remove-async-file.txt');
} catch (err) {
  // code for handling error 
}

The file removed succesfully from the path -tmp/test-fs-async/remove-async-file.txt

Node.js asynchronous ordering

In case of asynchronous execution, the ordering of methods is not guaranteed. In the below given example related to the file renaming, if we call fs.stat() operation before the fs.rename() then it could lead to error.

fs.rename('/tmp/test-fs-async/remove-async-file.txt', '/tmp/world', (err) => {
  if (err) throw err;
  fs.stat('/tmp/test-fs-async/sync-file.txt', (err, stats) => {
    if (err) throw err;
    console.log(`stats: ${JSON.stringify(stats)}`);
  });
});

Node.js File System Flags

The fs module provides below given syntax for opening the file

fs.open(path, flags[, mode], callback)    where
path: path string with the file name

flags: depicts the behavior of the file to be opened.

mode: sets the file mode if the file was created. It defaults to 0666, readable and writable.

callback: This is the callback function which gets two arguments (err, fd)

The below given are the commonly used file system flags.

File information using node.js file system

The below given syntax provides the file related information

fs.stat(path, callback)  , where

path: path string with the file name

callback: This is the callback function which gets two arguments (err, stats)

fs stats class methods in node.js file system

Node.js fs promises API

The node.js fs promises API provides and alternate approach than calling asynchronous file system methods. It returns the promise object than using the callbacks. The promises API can be accessed using the below given command:

require(‘fs’).promises