Node.js fs.close() Method

The fs.close() method is used to asynchronously close the given file descriptor thereby clearing the file that is associated with it. This will allow the file descriptor to be reused for other files. Calling fs.close() on a file descriptor while some other operation is being performed on it may lead to undefined behavior.

Syntax:

fs.close( fd, callback )

Parameters: This method accepts two parameters as mentioned above and described below:

• fd: It is an integer that denotes the file descriptor of the file for which to be closed.
• callback: It is a function that would be called when the method is executed.
  • err: It is an error that would be thrown if the method fails.

Below examples illustrate the fs.close() method in Node.js:

Example 1: This example shows the closing of a file descriptor.

// Node.js program to demonstrate the
// fs.close() method

// Import the filesystem module
const fs = require('fs');

// Get the file descriptor of the given path
file_descriptor = fs.openSync("example.txt");
console.log("The file descriptor is:", file_descriptor);

// Close the file descriptor
fs.close(file_descriptor, (err) => {
  if (err)
    console.error('Failed to close file', err);
  else {
    console.log("\n> File Closed successfully");
  }
});

Output:

The file descriptor is: 3

> File Closed successfully

Example 2: This example shows the closing of a file descriptor and trying to access that closed file descriptor again.

// Node.js program to demonstrate the
// fs.close() method

// Import the filesystem module
const fs = require('fs');

// Get the file descriptor of the given path
file_descriptor = fs.openSync("example.txt");
console.log("The file descriptor is:", file_descriptor);

console.log("\n> Finding the stats of the file");
try {

  // Attempting to find stats of file before closing
  statsObj = fs.fstatSync(file_descriptor);
  console.log("Stats of the file generated");

  // Closing the file descriptor
  console.log("\n> Closing the file descriptor");
  fs.close(file_descriptor, (err) => {
    if (err)
      console.error("Failed to close file", err);
    else {
      console.log("File Closed successfully");

      try {
        // Attempting to find stats of file after closing
        console.log("\n> Finding the stats of the file again");
        statsObj = fs.fstatSync(file_descriptor);
        console.log("Stats of the file generated");
      }
      catch (err) {
        console.error("Cannot find stats of file", err);
      }
    }
  });

} catch (err) {
  console.error("Cannot find stats of file", err);
}

Output:

The file descriptor is: 3

> Finding the stats of the file
Stats of the file generated

> Closing the file descriptor
File Closed successfully

> Finding the stats of the file again
Cannot find stats of file Error: EBADF: bad file descriptor, fstat
    at Object.fstatSync (fs.js:897:3)
    at G:\tutorials\nodejs-fs-close\index.js:42:23
    at FSReqCallback.oncomplete (fs.js:146:23) {
  fd: 3,
  errno: -4083,
  syscall: 'fstat',
  code: 'EBADF'
}

Reference: https://nodejs.org/api/fs.html#fs_fs_close_fd_callback