syntheticFid.js

const puppeteer = require('puppeteer');
// throttle network and cpu?
const throttle = true;
// viewport sizes
const viewportw = 412;
const viewporth = 732;
// url to test
const theurl = 'https://tamethebots.com';

(async() => {
    const browser = await puppeteer.launch();
    const page = await browser.newPage();
    const client = await page.target().createCDPSession()
    if (throttle) {
        await client.send('Network.emulateNetworkConditions', {
            'offline': false,
            'downloadThroughput': 1.5 * 1024 * 1024 / 8,
            'uploadThroughput': 750 * 1024 / 8,
            'latency': 40
        })
        await client.send('Emulation.setCPUThrottlingRate', { rate: 4 });
    }
    await page.setViewport({
        width: parseInt(viewportw),
        height: parseInt(viewporth)
    });
    try {
        await page.goto(theurl, {
            waitUntil: 'networkidle0'
        });
        await page.click('html')
        const metricsArray = await Promise.race([page.evaluate(() => {
                return new Promise(resolve => {
                    function sendFid(verdict) {
                        resolve(verdict);

                    }
                    new PerformanceObserver(list => {
                        list.getEntries().forEach(entry => {
                            FID = parseFloat(entry.processingStart - entry.startTime);
                            let ver = 'good';
                            if (FID > 100 && FID <= 300) {
                                ver = 'needs improvement';
                            }
                            if (FID > 300) {
                                ver = 'poor';
                            }

                            sendFid({
                                fid: `${FID.toFixed(4)} Ms`,
                                verdict: ver
                            });
                        });
                    }).observe({
                        type: 'first-input',
                        buffered: true
                    });

                });
            }),
            page.waitForTimeout(5000)
        ]);

        console.log(metricsArray);
        await browser.close();

    } catch (err) {
        console.log('Error loading page:', err);
        await browser.close();

    }


})();