fs Access Mode Constants Migration (DEP0176)

Migrate fs.F_OK, fs.R_OK, fs.W_OK, and fs.X_OK from root fs module to fs.constants

This recipe transforms imports of fs.F_OK, fs.R_OK, fs.W_OK, and fs.X_OK from the root fs module to fs.constants, addressing the deprecation of these constants at the module root level.

What It Does

The codemod transforms:

• fs.F_OK → fs.constants.F_OK
• fs.R_OK → fs.constants.R_OK
• fs.W_OK → fs.constants.W_OK
• fs.X_OK → fs.constants.X_OK

Usage

npx codemod nodejs/fs-access-mode-constants

Examples

Basic Usage

Before

const fs = require('node:fs');

fs.access('/path/to/file', fs.F_OK, callback);

After

const fs = require('node:fs');

fs.access('/path/to/file', fs.constants.F_OK, callback);

Combined Access Modes

Before

const fs = require('node:fs');

fs.access('/path/to/file', fs.R_OK | fs.W_OK, callback);

After

const fs = require('node:fs');

fs.access('/path/to/file', fs.constants.R_OK | fs.constants.W_OK, callback);

Multiple Checks

Before

import { access, F_OK, R_OK, X_OK } from 'node:fs';

access('/script.sh', F_OK, (err) => {
  if (!err) {
    access('/script.sh', X_OK, (err) => {
      console.log(err ? 'not executable' : 'executable');
    });
  }
});

After

import { access, constants } from 'node:fs';

access('/script.sh', constants.F_OK, (err) => {
  if (!err) {
    access('/script.sh', constants.X_OK, (err) => {
      console.log(err ? 'not executable' : 'executable');
    });
  }
});

Access Mode Constants

F_OK - File Existence

Checks if the file exists (without checking permissions):

import { access, constants } from 'node:fs/promises';

try {
  await access('/path/to/file', constants.F_OK);
  console.log('File exists');
} catch {
  console.log('File does not exist');
}

R_OK - Read Permission

Checks if the file is readable:

import { access, constants } from 'node:fs/promises';

try {
  await access('/path/to/file', constants.R_OK);
  console.log('File is readable');
} catch {
  console.log('File is not readable');
}

W_OK - Write Permission

Checks if the file is writable:

import { access, constants } from 'node:fs/promises';

try {
  await access('/path/to/file', constants.W_OK);
  console.log('File is writable');
} catch {
  console.log('File is not writable');
}

X_OK - Execute Permission

Checks if the file is executable:

import { access, constants } from 'node:fs/promises';

try {
  await access('/path/to/script.sh', constants.X_OK);
  console.log('File is executable');
} catch {
  console.log('File is not executable');
}

Why Migrate?

Access mode constants at the root fs module level were deprecated to improve API organization and consistency.

Moving to fs.constants:

• Groups related constants together
• Aligns with the location of other fs constants
• Provides better API organization
• Matches conventions used by other Node.js modules

Combining Access Modes

You can combine multiple access modes using the bitwise OR operator (|):

import { access, constants } from 'node:fs/promises';

// Check if file is both readable AND writable
try {
  await access('/path/to/file', constants.R_OK | constants.W_OK);
  console.log('File is readable and writable');
} catch {
  console.log('File is not readable and/or not writable');
}

fs.access() should not be used to check file accessibility before fs.open(). Instead, open the file directly and handle errors. Using access() first introduces a race condition.

Common Patterns

Check Before Read

import { access, readFile, constants } from 'node:fs/promises';

try {
  await access('/config.json', constants.R_OK);
  const data = await readFile('/config.json', 'utf8');
  console.log(JSON.parse(data));
} catch (err) {
  console.error('Cannot read config:', err.message);
}

Verify Multiple Files

import { access, constants } from 'node:fs/promises';

const files = ['file1.txt', 'file2.txt', 'file3.txt'];

const results = await Promise.allSettled(
  files.map(file => access(file, constants.F_OK))
);

results.forEach((result, i) => {
  if (result.status === 'fulfilled') {
    console.log(`${files[i]} exists`);
  } else {
    console.log(`${files[i]} does not exist`);
  }
});

Other fs.constants

The fs.constants object also includes:

• File Open Flags: O_RDONLY, O_WRONLY, O_RDWR, etc.
• File Copy Flags: COPYFILE_EXCL, COPYFILE_FICLONE, etc.
• File Type Constants: S_IFMT, S_IFREG, S_IFDIR, etc.

Deprecation Reference

This migration addresses DEP0176.