howToWriteToLogAndReadFromIt.js

const express = require('express');
const fs = require("fs");
const readline = require("readline");
const app = express();
const port = 3003;
let ip;
let userName;

// Process JSON in request body
app.use(express.json());

// Store IP
app.use(function (req, res, next) {
    ip = req.headers['x-forwarded-for'] || req.socket.remoteAddress;
    next();
});

// Log the event to file
function log(eventName, extraData) {

    // Create timestamp
    const timeStamp = new Date().toISOString().replace(/T/, ' ').replace(/\..+/, '')

    // Parse extraData to JSON and escape commas with backslash
    extraData = JSON.stringify(extraData).replace(/,/g, '\\,');

    // Write to file
    fs.appendFile('log.txt', timeStamp + ',' + ip + ',' + userName + ',' + eventName + ',' + extraData + ' \r\n', function (err) {
        if (err) throw err;
    });
}

app.get('/logs', async (req, res) => {

    // Log a random test event
    log('testEvent', {message: 'logs,logs,logs'});

    // Read the log file
    const lines = [];
    const lineReader = readline.createInterface({
        input: fs.createReadStream('log.txt'),
        crlfDelay: Infinity
    });

    // Parse the log file
    for await (const line of lineReader) {

        // Split the line into array with comma as delimiter, except when comma is escaped with backslash
        const fields = line.match(/(\\.|[^,])+/g)

        // Iterate over result
        for (let i = 0; i < fields.length; i++) {

            // Remove backslash from escaped commas
            fields[i] = fields[i].replace(/\\/g, '');
        }

        // Add the line to the lines array
        lines.push({
            timestamp: fields[0],
            ip: fields[1],
            userName: fields[2],
            eventName: fields[3],
            extraData: fields[4]
        });
    }

    // Return the lines array
    return res.send(lines);

})

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

YOU MUST TAKE CARE OF SETTING THE USERNAME YOURSELF