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@addyosmani

addyosmani/lcp.js

Last active Nov 1, 2020
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Largest Contentful Paint - Puppeteer
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'];
function calcLCP() {
window.largestContentfulPaint = 0;
const observer = new PerformanceObserver((entryList) => {
const entries = entryList.getEntries();
const lastEntry = entries[entries.length - 1];
window.largestContentfulPaint = lastEntry.renderTime || lastEntry.loadTime;
});
observer.observe({ type: 'largest-contentful-paint', buffered: true });
document.addEventListener('visibilitychange', () => {
if (document.visibilityState === 'hidden') {
observer.takeRecords();
observer.disconnect();
console.log('LCP:', window.largestContentfulPaint);
}
});
}
async function getLCP(url) {
const browser = await puppeteer.launch({
args: ['--no-sandbox'],
timeout: 10000
});
try {
const page = await browser.newPage();
const client = await page.target().createCDPSession();
await client.send('Network.enable');
await client.send('ServiceWorker.enable');
await client.send('Network.emulateNetworkConditions', Good3G);
await client.send('Emulation.setCPUThrottlingRate', { rate: 4 });
await page.emulate(phone);
await page.evaluateOnNewDocument(calcLCP);
await page.goto(url, { waitUntil: 'load', timeout: 60000 });
let lcp = await page.evaluate(() => {
return window.largestContentfulPaint;
});
return lcp;
browser.close();
} catch (error) {
console.log(error);
browser.close();
}
}
getLCP("https://pptr.dev").then(lcp => console.log("LCP is: " + lcp));
@warpech

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@warpech warpech commented Aug 5, 2020

Hi Addy! This is very useful. Could you please add license information?

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