nodejs-stream-batch-processing.js

`use strict`;

const COLUMN_DELIMITER = ';'
const LINE_DELIMITER = '\n';
const SOURCE_FILE = 'sample.txt';
const OUTPUT_FILE = 'output.txt';

const fs = require('fs');
const buffer = [];

const readCallback = (err, contents) => {
    if (err) {
        console.error('Read was failed. Err: ' + err);
        return;
    }

    const lines = contents.toString().split(LINE_DELIMITER);
    
    for (let i =  0; i < lines.length-1; i++) {
        const line = lines[i];

        const row = line.split(COLUMN_DELIMITER);
        const trimmedRow = trimProcessor(row);
        const processedRow = nameProcessor(trimmedRow);
        
        buffer.push(processedRow.join(COLUMN_DELIMITER));
    }
    
    fs.writeFile(OUTPUT_FILE, buffer.join(LINE_DELIMITER), writeCallback);
}

const writeCallback = (err) => {
    if (err) {
        console.error('Write was failed. Err: ' + err);
        return;
    }

    console.log('The process has been completed.');
}

const trimProcessor = (row) => {
    const clonnedRow = Array.from(row);
    return clonnedRow.map(column => column.trim());
}

const nameProcessor = (row) => {
    const clonnedRow = Array.from(row);

    const firstName = clonnedRow[0].toUpperCase();
    const lastName = clonnedRow[1].toUpperCase();

    const fullName = firstName + ' ' + lastName;

    clonnedRow.splice(0, 2, fullName);

    return clonnedRow;
}

fs.readFile(SOURCE_FILE, readCallback);