longtasks_via_cdp.js

const puppeteer = require('puppeteer');
const devices = require('puppeteer/DeviceDescriptors');

const Good3G = {
    'offline': false,
    'downloadThroughput': 1.5 * 1024 * 1024 / 8,
    'uploadThroughput': 750 * 1024 / 8,
    'latency': 40
  };
  
const phone = devices['Nexus 5X'];



async function run(url) {
	// I can't get the experimental flag working on chromium, so let's start system chrome
    const browser = await puppeteer.launch({headless: true});	
    let page = await browser.newPage();
    const client = await page.target().createCDPSession();
    await client.send('Network.enable');
    await client.send('Network.emulateNetworkConditions', Good3G);
    await client.send('Emulation.setCPUThrottlingRate', { rate: 20 });
	await page.emulate(phone);
	
	await client.send('Log.enable');
	await client.send('Log.startViolationsReport', {config:[{name: "longTask", threshold: 0.005}]});
	
	client.on('Log.entryAdded', async (entry) => {
		//if(entry.entry.source!=="javascript") return;
		console.log(JSON.stringify(entry.entry, null, 2));
	});
	
	// load page
	await page.goto(url, {"timeout": "120000"});
		
    await page.close();
    await browser.close();
}

run("https://www.spiegel.de");