perf.js

const timing    = performance.timing
const navStart  = timing.navigationStart
const ttfb      = timing.responseStart - navStart
const dclStart  = timing.domContentLoadedEventStart - navStart
const dclEnd    = timing.domContentLoadedEventEnd - navStart
const resources = performance.getEntriesByType('resource')
const delayDCL  = resources.filter((res) => res.responseEnd < dclStart)