index.js

#!/usr/bin/env node

const lighthouse = require('lighthouse'),
    chromeLauncher = require('chrome-launcher'),
    queue = require('async/queue'),
    cTable = require('console.table'),
    loadingSpinner = require('loading-spinner'),
    program = require('commander'),
    packageJson = require('./package.json');

var allResults = [[],[]];
var config = {
    instances: 5,
    iterations: 5
}

function launchChromeAndRunLighthouse(url, config = null) {
    const opts = {chromeFlags: ['--headless']};
    return chromeLauncher.launch({chromeFlags: opts.chromeFlags}).then(chrome => {
        opts.port = chrome.port;
        return lighthouse(url, opts, config).then(results => {
            return chrome.kill().then(() => results.lhr)
        });
    });
}

function toTitleCase(str) {
    return str.replace(/-/g, ' ').replace(/\w\S*/g, function(txt){
        return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();
    });
}

function begin(url1, url2){
    loadingSpinner.start(100, { clearChar: true, doNotBlock: true });

    config.iterations = program.number || number;
    config.instances = program.instances || instances;

    const lighthouseQueue = queue((endpoint, callback) => {
        launchChromeAndRunLighthouse(endpoint.url).then(function(results) {
            allResults[endpoint.version].push(results);
            callback()
        });
    }, config.instances)

    lighthouseQueue.drain = function() {
        loadingSpinner.stop();

        var table = [], arr = ['first-meaningful-paint', 'first-contentful-paint', 'speed-index', 'estimated-input-latency', 'time-to-first-byte', 
        'first-cpu-idle', 'interactive', 'mainthread-work-breakdown', 'bootup-time', 'network-requests', 'total-byte-weight', 'unused-css-rules'];

        arr.forEach( function(string) {
            var before = Math.round(allResults[0].reduce((a,c) => (c['audits'][string]['rawValue'] + a), 0) / allResults[0].length);
            var after = Math.round(allResults[1].reduce((a,c) => (c['audits'][string]['rawValue'] + a), 0) / allResults[0].length);
            var difference = -((before - after) / before * 100).toFixed(2);
            var tableData = {};

            tableData["Metric"]     = toTitleCase(string);
            tableData['Url 1']      = before;
            tableData['Url 2']      = after;
            tableData["Difference"] = difference > 0 ? '+' + difference + '%' : difference + '%';

            table.push(tableData);
        });

        console.log('\n');
        console.table(table);
    };

    for(var x = 0; x < config.iterations; x++){
        lighthouseQueue.push({url: url1, version: 0})
        lighthouseQueue.push({url: url2, version: 1})
    }
}

program
    .version(packageJson.version)
    .arguments('<url1> <url2>')
    .option('-n, --number <number>', 'The number of times both URL\'s should be run in lighthouse (default: 5)')
    .option('-o, --one <one>', 'The title of the first URL tested')
    .option('-t, --two <two>', 'The title of the second URL tested')
    .option('-i, --instances <instances>', 'The number lighthouse instances used at once (default: 5)')
    .action(begin)
    .parse(process.argv);