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In this section, we will explore the File System (fs) module in Node.js, which allows you to interact with the file system on your computer. This module provides a variety of methods to read, write, update, delete, and manipulate files and directories.

Key Concepts

Synchronous vs Asynchronous Methods:
- Synchronous methods block the execution of code until the operation is complete.
- Asynchronous methods do not block the execution and use callbacks or promises to handle the result.
Common Operations:
- Reading files
- Writing files
- Appending to files
- Deleting files
- Working with directories

Importing the File System Module

To use the File System module, you need to import it using the require function:

const fs = require('fs');

Reading Files

Asynchronous Reading

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log('File content:', data);
});

Synchronous Reading

try {
  const data = fs.readFileSync('example.txt', 'utf8');
  console.log('File content:', data);
} catch (err) {
  console.error('Error reading file:', err);
}

Writing Files

Asynchronous Writing

const content = 'Hello, World!';
fs.writeFile('example.txt', content, 'utf8', (err) => {
  if (err) {
    console.error('Error writing file:', err);
    return;
  }
  console.log('File written successfully');
});

Synchronous Writing

const content = 'Hello, World!';
try {
  fs.writeFileSync('example.txt', content, 'utf8');
  console.log('File written successfully');
} catch (err) {
  console.error('Error writing file:', err);
}

Appending to Files

Asynchronous Appending

const additionalContent = '\nAppended content';
fs.appendFile('example.txt', additionalContent, 'utf8', (err) => {
  if (err) {
    console.error('Error appending to file:', err);
    return;
  }
  console.log('Content appended successfully');
});

Synchronous Appending

const additionalContent = '\nAppended content';
try {
  fs.appendFileSync('example.txt', additionalContent, 'utf8');
  console.log('Content appended successfully');
} catch (err) {
  console.error('Error appending to file:', err);
}

Deleting Files

Asynchronous Deletion

fs.unlink('example.txt', (err) => {
  if (err) {
    console.error('Error deleting file:', err);
    return;
  }
  console.log('File deleted successfully');
});

Synchronous Deletion

try {
  fs.unlinkSync('example.txt');
  console.log('File deleted successfully');
} catch (err) {
  console.error('Error deleting file:', err);
}

Working with Directories

Creating a Directory

Asynchronous Creation

fs.mkdir('newDir', { recursive: true }, (err) => {
  if (err) {
    console.error('Error creating directory:', err);
    return;
  }
  console.log('Directory created successfully');
});

Synchronous Creation

try {
  fs.mkdirSync('newDir', { recursive: true });
  console.log('Directory created successfully');
} catch (err) {
  console.error('Error creating directory:', err);
}

Reading a Directory

Asynchronous Reading

fs.readdir('newDir', (err, files) => {
  if (err) {
    console.error('Error reading directory:', err);
    return;
  }
  console.log('Directory contents:', files);
});

Synchronous Reading

try {
  const files = fs.readdirSync('newDir');
  console.log('Directory contents:', files);
} catch (err) {
  console.error('Error reading directory:', err);
}

Deleting a Directory

Asynchronous Deletion

fs.rmdir('newDir', { recursive: true }, (err) => {
  if (err) {
    console.error('Error deleting directory:', err);
    return;
  }
  console.log('Directory deleted successfully');
});

Synchronous Deletion

try {
  fs.rmdirSync('newDir', { recursive: true });
  console.log('Directory deleted successfully');
} catch (err) {
  console.error('Error deleting directory:', err);
}

Practical Exercise

Task

Create a new directory named testDir.
Inside testDir, create a file named testFile.txt and write some content to it.
Append additional content to testFile.txt.
Read and log the content of testFile.txt.
Delete testFile.txt.
Delete testDir.

Solution

const fs = require('fs');

// Step 1: Create a new directory
fs.mkdir('testDir', { recursive: true }, (err) => {
  if (err) {
    console.error('Error creating directory:', err);
    return;
  }
  console.log('Directory created successfully');

  // Step 2: Create a file and write content
  fs.writeFile('testDir/testFile.txt', 'Initial content', 'utf8', (err) => {
    if (err) {
      console.error('Error writing file:', err);
      return;
    }
    console.log('File written successfully');

    // Step 3: Append additional content
    fs.appendFile('testDir/testFile.txt', '\nAppended content', 'utf8', (err) => {
      if (err) {
        console.error('Error appending to file:', err);
        return;
      }
      console.log('Content appended successfully');

      // Step 4: Read and log the content
      fs.readFile('testDir/testFile.txt', 'utf8', (err, data) => {
        if (err) {
          console.error('Error reading file:', err);
          return;
        }
        console.log('File content:', data);

        // Step 5: Delete the file
        fs.unlink('testDir/testFile.txt', (err) => {
          if (err) {
            console.error('Error deleting file:', err);
            return;
          }
          console.log('File deleted successfully');

          // Step 6: Delete the directory
          fs.rmdir('testDir', { recursive: true }, (err) => {
            if (err) {
              console.error('Error deleting directory:', err);
              return;
            }
            console.log('Directory deleted successfully');
          });
        });
      });
    });
  });
});

Conclusion

In this section, we covered the basics of the File System module in Node.js, including how to read, write, append, and delete files, as well as how to work with directories. Understanding these operations is crucial for handling file I/O in your Node.js applications. In the next module, we will delve into working with streams, which provide a more efficient way to handle large files and data streams.

File System Module

Key Concepts

Importing the File System Module

Reading Files

Asynchronous Reading

Synchronous Reading

Writing Files

Asynchronous Writing

Synchronous Writing

Appending to Files

Asynchronous Appending

Synchronous Appending

Deleting Files

Asynchronous Deletion

Synchronous Deletion

Working with Directories

Creating a Directory

Asynchronous Creation

Synchronous Creation

Reading a Directory

Asynchronous Reading

Synchronous Reading

Deleting a Directory

Asynchronous Deletion

Synchronous Deletion

Practical Exercise

Task

Solution

Conclusion

Node.js Course

Module 1: Introduction to Node.js

Module 2: Core Concepts

Module 3: File System and I/O

Module 4: HTTP and Web Servers

Module 5: NPM and Package Management

Module 6: Express.js Framework

Module 7: Databases and ORMs

Module 8: Authentication and Authorization

Module 9: Testing and Debugging

Module 10: Advanced Topics

Module 11: Deployment and DevOps

Module 12: Real-World Projects