1.File System

CommonJS (CJS) vs. ECMAScript Modules (ESM)

CommonJS Syntax

Importing Modules:
- To use a module, assign it to a constant:
```
const fs = require('fs');
```

File System Operations

Using the fs module, you can perform various file operations:

Write to a File:

fs.writeFile('hey.txt', "helloworld", function(err) {
    if (err) console.error(err);
    else console.log("File written successfully.");
});

Append to a File:

fs.appendFile("hey.txt", " this is new", function(err) {
    if (err) console.error(err);
    else console.log("Content appended successfully.");
});

Rename a File:

fs.rename("hey.txt", "hello.txt", function(err) {
    if (err) console.error(err);
    else console.log("File renamed successfully.");
});

Copy a File:

To copy a file, you can use fs.copyFile (Node.js 8.5.0 and above):

fs.copyFile('source.txt', 'destination.txt', (err) => {
    if (err) console.error(err);
    else console.log('File copied successfully.');
});

Delete a File (Unlink):

fs.unlink("hello.txt", function(err) {
    if (err) console.error(err);
    else console.log("File deleted successfully.");
});

6. Delete a Directory

Removing an Empty Directory:

fs.rmdir("./foldername", function(err) {
    if (err) console.log(err);
    else console.log("Directory removed successfully.");
});

Note: fs.rmdir cannot remove directories that contain files. Attempting to do so will result in an error.

Removing a Directory Recursively:
- To delete a directory along with its contents (files and subdirectories), use fs.rm with the recursive option:
```
fs.rm("./foldername", { recursive: true }, function(err) {
    if (err) console.log(err);
    else console.log("Directory and its contents removed successfully.");
});
```
- Note: The default value for recursive is false, so you must specify it as true for recursive deletion.

7. Create a Folder

To create a new directory:

fs.mkdir("./newFolder", { recursive: true }, function(err) {
    if (err) console.log(err);
    else console.log("Directory created successfully.");
});

The recursive: true option allows the creation of nested directories without error if the parent directory already exists.

8. Read a File

To read the contents of a file:

fs.readFile('file.txt', 'utf8', function(err, data) {
    if (err) console.log(err);
    else console.log(data);  // Displays the content of the file
});

9. Read Folder Contents

To read the contents of a directory:

fs.readdir('./foldername', function(err, files) {
    if (err) console.log(err);
    else {
        console.log("Directory contents:");
        files.forEach(file => {
            console.log(file);
        });
    }
});