How to measure Web Core Vital in puppeteer

To measure Web Core Vitals using Puppeteer, you can leverage Puppeteer to collect performance metrics and then interpret those metrics to determine the Core Web Vitals. Here’s a high-level approach to achieve this:

Steps to Measure Web Core Vitals with Puppeteer

1. Install Dependencies: Ensure you have Puppeteer installed in your project:

   npm install puppeteer
   

2. Write Puppeteer Script: Create a script that launches Puppeteer, navigates to a URL, collects performance metrics, and calculates Core Web Vitals.

   const puppeteer = require('puppeteer');
   
   (async () => {
     const browser = await puppeteer.launch();
     const page = await browser.newPage();
   
     // URL to analyze
     const url = 'https://example.com';
   
     // Navigate to the page
     await page.goto(url, { waitUntil: 'networkidle2' });
   
     // Wait for the page to settle and collect metrics
     const metrics = await page.evaluate(() => {
       return {
         // Use Navigation Timing API to get metrics
         navigationTiming: JSON.parse(JSON.stringify(performance.timing)),
         // Other custom metrics you may want to collect
         // For Core Web Vitals:
         // 1. Largest Contentful Paint (LCP)
         // 2. Cumulative Layout Shift (CLS)
         // 3. First Input Delay (FID)
       };
     });
   
     // Calculate Core Web Vitals from collected metrics
     const lcp = metrics.navigationTiming.loadEventEnd - metrics.navigationTiming.loadEventStart;
     const cls = calculateCLS(); // Implement function to calculate Cumulative Layout Shift
     const fid = calculateFID(); // Implement function to calculate First Input Delay
   
     // Output Core Web Vitals
     console.log('Largest Contentful Paint (LCP):', lcp);
     console.log('Cumulative Layout Shift (CLS):', cls);
     console.log('First Input Delay (FID):', fid);
   
     await browser.close();
   })();
   

   • Replace 'https://example.com' with the URL of the website you want to analyze.

3. Calculate Core Web Vitals: Implement functions (calculateCLS, calculateFID, etc.) to interpret the collected metrics into Core Web Vitals. For example, Cumulative Layout Shift (CLS) can be calculated by listening to layout shift events using the LayoutInstability API in your Puppeteer script.

4. Run the Script: Execute your Puppeteer script to launch a headless Chrome instance, navigate to the specified URL, collect metrics, calculate Core Web Vitals, and output the results:

   node web-vitals.js
   

Notes:

• Custom Metrics: Besides Core Web Vitals (LCP, CLS, FID), you can collect other metrics like Time to First Byte (TTFB), Total Blocking Time (TBT), etc., using Puppeteer and relevant APIs.

• Performance APIs: Puppeteer uses the browser’s Performance APIs (like Navigation Timing API, LayoutInstability API, etc.) to gather metrics. These APIs provide detailed information about page load and interaction timings.

• Integration: Incorporate this approach into your testing or monitoring workflows to continuously measure and optimize Core Web Vitals for better user experience and SEO performance.