lcp.ts

let lcp = await page.evaluate(() => new Promise((resolve, reject) => {
            try {
                // Create a variable to hold the latest LCP value (since it can change).
                let lcp;

                // Create the PerformanceObserver instance.
                const po = new PerformanceObserver((entryList) => {
                    const entries = entryList.getEntries();
                    const lastEntry = entries[entries.length - 1];

                    lcp = (<any>lastEntry).renderTime || (<any>lastEntry).loadTime;
                    resolve(lcp);
                    po.disconnect();
                });

                // Observe entries of type `largest-contentful-paint`, including buffered
                // entries, i.e. entries that occurred before calling `observe()`.
                po.observe({ type: 'largest-contentful-paint', buffered: true });
            } catch (e) {
                // Do nothing if the browser doesn't support this API.
            }
        }));
        console.log('lcp is',lcp);