Node.js Шпаргалка по API FS Open, Read, Write, Close

const fs = require('fs');

// Read file

const filePath1 = 'test-file1.txt';

fs.open(filePath1, 'r', function (error, fd) {
    if (error) {throw error;}
    console.log('File 1 opened');
    fs.fstat(fd, function (error, stat) {
        if (error) {throw error;}

        const fileSize = stat.size;
        let chunkSize = 2; // 512; // in bytes

        let fileBuffer = Buffer.alloc(fileSize);
        let totalBytesRead = 0;

        function readDataFromFile () {
            if (totalBytesRead < fileSize) {
                if ((totalBytesRead + chunkSize) > fileSize) {
                    chunkSize = fileSize - totalBytesRead;
                }
                fs.read(fd, fileBuffer, totalBytesRead, chunkSize, totalBytesRead, function (error, chunkBytesRead, buffer) {
                    if (error) {throw error;}
                    totalBytesRead += chunkSize;
                    console.log(buffer.toString('utf8', 0, fileSize));
                    readDataFromFile();
                });
            } else {
                fs.close(fd, function (error) {
                    if (error) {throw error;}
                    console.log('File 1 closed');
                });
            }
        }
        readDataFromFile();
    });
});

// Write file from string

const filePath2 = 'test-file2.txt';

fs.open(filePath2, 'w', function (error, fd) {
    if (error) {throw error;}
    console.log('File 2 opened');
    fs.fstat(fd, function (error, stat) {
        if (error) {throw error;}

        const data = 'abcdefghijklmnopqrstuvwxyz';
        let chunkSize = 1; // in characters

        const dataSize = data.length;
        let totalCharactersWritten = 0;

        let chunk = data.slice(0, chunkSize);

        function writeDataToFile () {
            if (totalCharactersWritten < dataSize) {
                fs.write(fd, chunk, totalCharactersWritten, 'utf8', function (error, chunkCharactersWritten, string) {
                    if (error) {throw error;}
                    totalCharactersWritten += chunk.length;
                    console.log(string);
                    if ((totalCharactersWritten + chunkSize) > dataSize) {
                        chunkSize = dataSize - totalCharactersWritten;
                    }
                    chunk = data.slice(totalCharactersWritten, totalCharactersWritten + chunkSize);
                    writeDataToFile();
                });
            } else {
                fs.close(fd, function (error) {
                    if (error) {throw error;}
                    console.log('File 2 closed');
                });
            }
        }
        writeDataToFile();
    });
});

// Write file from buffer

const filePath3 = 'test-file2.txt';

fs.open(filePath3, 'w', function (error, fd) {
    if (error) {throw error;}
    console.log('File 3 opened');
    fs.fstat(fd, function (error, stat) {
        if (error) {throw error;}

        const data = Buffer.from('abcdefghijklmnopqrstuvwxyz');
        let chunkSize = 2; // in bytes

        const dataSize = data.length;
        let totalBytesWritten = 0;

        let chunk = data.slice(0, chunkSize);

        function writeDataToFile () {
            if (totalBytesWritten < dataSize) {
                fs.write(fd, chunk, 0, chunkSize, totalBytesWritten, function (error, chunkBytesWritten, buffer) {
                    if (error) {throw error;}
                    totalBytesWritten += chunkSize;
                    console.log(buffer.toString('utf8'));
                    if ((totalBytesWritten + chunkSize) > dataSize) {
                        chunkSize = dataSize - totalBytesWritten;
                    }
                    chunk = data.slice(totalBytesWritten, totalBytesWritten + chunkSize);
                    writeDataToFile();
                });
            } else {
                fs.close(fd, function (error) {
                    if (error) {throw error;}
                    console.log('File 3 closed');
                });
            }
        }
        writeDataToFile();
    });
});