experimental-sample3.js

'use strict';
const {
  performance,
  PerformanceObserver
} = require('perf_hooks');
const request = require("request")

function queryEngines(done) {
    const urls = [
        "http://www.google.com",
        "http://yahoo.com",
        "http://bing.com",
        "http://duckduckgo.com"
    ]

    let results = []

    urls.forEach( (url) => {
        performance.mark(url + "-init") //initial mark for the current URL
        
        request(url, (err, cnt) => {
            performance.mark(url + "-end") //final mark for the same URL
            performance.measure(url, url + "-init", url + "-end") //calculate the time difference between the start and end 

            results.push(cnt)
            if(results.length === urls.length) {
                return done(results)
            }
        })
    })
}

// Activate the observer
const obs = new PerformanceObserver((list) => {
  const entry = list.getEntries()[0]
  console.log(`Time for ('${entry.name}')`, entry.duration);
});
obs.observe({ entryTypes: ['measure'], buffered: false});  //we want to react to full measurements and not individual marks

queryEngines( (pages) => {
    console.log("Done!")
})