In contemporary Node.js development, the fsPromises API is increasingly favored over the traditional fs module. This preference stems from its superior integration with modern JavaScript features, particularly async/await, which enhances code readability and maintainability, especially in complex scenarios.

Why fsPromises is Preferred

1. Async/Await Compatibility

fsPromises seamlessly integrates with async/await, allowing asynchronous code to be structured in a more synchronous, intuitive manner.

const fs = require('fs').promises;

async function readAndProcessFile() {
    try {
        const data = await fs.readFile('input.txt', 'utf8');
        const processedData = data.toUpperCase();
        await fs.writeFile('output.txt', processedData);
        console.log('File processed successfully');
    } catch (err) {
        console.error('Error processing file:', err);
    }
}

readAndProcessFile();

2. Simplified Error Handling

With async/await and fsPromises, error handling becomes more straightforward using try/catch blocks, mirroring synchronous code structures.

const fs = require('fs').promises;

async function copyFile(source, destination) {
    try {
        await fs.copyFile(source, destination);
        console.log(`${source} was copied to ${destination}`);
    } catch (err) {
        console.error('Error copying file:', err);
    }
}

copyFile('source.txt', 'destination.txt');

3. Avoidance of Callback Hell

Traditional fs methods rely on callbacks, which can lead to deeply nested, hard-to-read code when dealing with multiple asynchronous operations. fsPromises resolves this issue by returning promises, which can be chained or managed with async/await.

// Traditional fs (callback hell)
fs.readdir('directory', (err, files) => {
    if (err) throw err;
    files.forEach((file) => {
        fs.readFile(`directory/${file}`, 'utf8', (err, content) => {
            if (err) throw err;
            fs.writeFile(`processed/${file}`, content.toUpperCase(), (err) => {
                if (err) throw err;
                console.log(`Processed ${file}`);
            });
        });
    });
});

// Using fsPromises
const fs = require('fs').promises;

async function processDirectory() {
    try {
        const files = await fs.readdir('directory');
        for (const file of files) {
            const content = await fs.readFile(`directory/${file}`, 'utf8');
            await fs.writeFile(`processed/${file}`, content.toUpperCase());
            console.log(`Processed ${file}`);
        }
    } catch (err) {
        console.error('Error processing directory:', err);
    }
}

processDirectory();

4. Improved Code Consistency

Utilizing fsPromises promotes consistency across your codebase, especially in projects that extensively use promises or async/await for other asynchronous operations.

5. Better Performance in Some Scenarios

While the performance difference is often negligible, fsPromises can lead to more efficient code execution in scenarios involving multiple asynchronous operations, as it avoids the overhead of managing numerous callbacks.

When is fs Still Relevant?

Despite the advantages of fsPromises, there are scenarios where the traditional fs module remains relevant:

1. Legacy Codebases: Older projects that haven't been updated might still rely on callback-based fs methods.

2. Simple Scripts: For quick, one-off scripts where the additional abstraction of promises isn't necessary, fs might be more straightforward.

3. Specific Streaming Operations: Some advanced streaming operations are still primarily supported through the traditional fs module.

4. Performance-Critical Low-Level Operations: In rare cases where absolute minimal overhead is required, the traditional fs methods might be preferred.

5. Compatibility with Older Node.js Versions: If supporting older Node.js versions is a requirement, the traditional fs module ensures wider compatibility.

Best Practices

1. Consistent API Usage: Choose either fsPromises or fs for a project and stick to it consistently to maintain code coherence.

2. Error Handling: Always implement proper error handling, regardless of which API you use.

3. Asynchronous Operations: Prefer asynchronous methods over synchronous ones to avoid blocking the event loop, especially in server environments.

4. Promisification: If you need to use the traditional fs module, consider using util.promisify() to convert callback-based methods into promise-based ones.
   

const fs = require('fs');
const util = require('util');
const readFile = util.promisify(fs.readFile);

async function readFileContent() {
    try {
        const content = await readFile('example.txt', 'utf8');
        console.log(content);
    } catch (err) {
        console.error('Error reading file:', err);
    }
}

Conclusion

For most modern Node.js applications, fsPromises is the recommended choice due to its compatibility with async/await, improved readability, and easier error handling. However, the traditional fs module still has its place, especially in legacy systems, simple scripts, or specific use cases requiring low-level control. When starting a new project or refactoring an existing one, consider adopting fsPromises to leverage the full power of modern JavaScript features in your file system operations.