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File Stats & Information

Imagine you're a detective examining a file. You want to know how old it is, how big it is, who owns it, and whether it's a file or a folder. In Node.js, the `fs.stat()` method gives you all this detective information about files and directories.

What are File Stats?

File stats provide detailed information about a file or directory:
  • Size – How many bytes
  • Creation time – When it was created
  • Modification time – When it was last changed
  • Access time – When it was last read
  • Permissions – Who can read/write/execute
  • Type – File, directory, symlink, etc.

Think of `fs.stat()` as the file's ID card – it tells you everything about the file's identity and history.

Getting File Stats (fs.stat)
const fs = require('fs');

fs.stat('sample.txt', (err, stats) => {
  if (err) {
    console.error('Error getting stats:', err);
    return;
  }
  
  console.log(stats);
});

Stats Object Properties

PropertyDescription
`stats.size`File size in bytes
`stats.birthtime`File creation timestamp
`stats.mtime`Last modification timestamp
`stats.atime`Last access timestamp
`stats.ctime`Status change timestamp (permissions, ownership)
`stats.mode`File permissions (as a number)
`stats.uid`User ID of owner
`stats.gid`Group ID of owner

Checking File Type

Stats provides methods to check what kind of filesystem object you're dealing with.
fs.stat('sample.txt', (err, stats) => {
  if (err) {
    console.error(err);
    return;
  }
  
  console.log('Is file?', stats.isFile());      <!-- true if file -->
  console.log('Is directory?', stats.isDirectory()); <!-- true if folder -->
  console.log('Is symbolic link?', stats.isSymbolicLink());
});

Reading File Sizes

Get file size in a human-readable format.
function formatBytes(bytes, decimals = 2) {
  if (bytes === 0) return '0 Bytes';
  
  const k = 1024;
  const dm = decimals < 0 ? 0 : decimals;
  const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
  
  const i = Math.floor(Math.log(bytes) / Math.log(k));
  
  return parseFloat((bytes / Math.pow(k, i)).toFixed(dm)) + ' ' + sizes[i];
}

fs.stat('large-file.zip', (err, stats) => {
  if (err) throw err;
  console.log('File size:', formatBytes(stats.size));
});

Working with Timestamps
fs.stat('document.pdf', (err, stats) => {
  if (err) throw err;
  
  console.log('Created:', stats.birthtime);
  console.log('Modified:', stats.mtime);
  console.log('Accessed:', stats.atime);
  
  <!-- Calculate age in days -->
  const ageMs = Date.now() - stats.birthtime;
  const ageDays = Math.floor(ageMs / (1000 * 60 * 60 * 24));
  console.log('File age:', ageDays, 'days');
});

File Permissions

The `stats.mode` contains permission information in numeric format.
fs.stat('script.sh', (err, stats) => {
  if (err) throw err;
  
  <!-- Convert mode to octal for readable permissions -->
  const mode = stats.mode.toString(8);
  console.log('Permissions (octal):', mode);
  
  <!-- Check if file is executable for owner -->
  const isExecutable = !!(stats.mode & fs.constants.S_IXUSR);
  console.log('Is executable?', isExecutable);
});

Using Promises with fs.stat
const fs = require('fs').promises;

async function getFileInfo(filePath) {
  try {
    const stats = await fs.stat(filePath);
    
    console.log(`File: ${filePath}`);
    console.log(`Size: ${stats.size} bytes`);
    console.log(`Created: ${stats.birthtime}`);
    console.log(`Is directory: ${stats.isDirectory()}`);
  } catch (err) {
    console.error(`Error getting stats for ${filePath}:`, err.message);
  }
}

getFileInfo('sample.txt');

Practical Example: File Cleanup by Age

Delete files older than 30 days.
const fs = require('fs').promises;
const path = require('path');

async function cleanOldFiles(directory, maxAgeDays = 30) {
  try {
    const files = await fs.readdir(directory);
    const now = Date.now();
    const maxAgeMs = maxAgeDays * 24 * 60 * 60 * 1000;
    
    for (const file of files) {
      const filePath = path.join(directory, file);
      const stats = await fs.stat(filePath);
      
      if (stats.isFile() && (now - stats.mtime) > maxAgeMs) {
        await fs.unlink(filePath);
        console.log(`Deleted old file: ${file}`);
      }
    }
  } catch (err) {
    console.error('Cleanup error:', err);
  }
}

cleanOldFiles('./logs', 7); <!-- Delete log files older than 7 days -->

Two Minute Drill

  • `fs.stat()` gives you detailed information about files and directories.
  • Use `stats.isFile()` and `stats.isDirectory()` to check type.
  • Access timestamps: `birthtime` (creation), `mtime` (modification), `atime` (access).
  • File size is in bytes – convert to human-readable format as needed.
  • Permissions are in `stats.mode` – use bitwise operations to check.
  • Always use try/catch with promises or check errors in callbacks.
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