Get Page performance result by Combining User and Resource timing API

 //calculate page loading time by resource timing API  
 var perfEntries = performance.getEntries();  
 var end_probe = perfEntries.filter(function(item) {  
   //page load finish request indicator  
   if (item.name.indexOf('/req_url_end') > -1) {  
     console.log(item.name);  
     return true;  
   }  
 });  
 if(end_probe.length > 0) {  
   var end_time = end_probe[0].responseEnd;  
   var start_probe = perfEntries.filter(function(item) {  
     //page load start indicator  
     if (item.name.indexOf('/req_url_start') > -1) {  
       console.log(item.name);  
       return true;  
     }  
   });  
   var start_time = start_probe[0].startTime;  
   var duration = end_time - start_time;  
   console.log(duration);  
 } else {  
   console.log("page loading end indicator is not found, please double check all perf Entries");  
 }  

There is a better way to combine User Timing API and Resource Timing API to get accurate page performance, i am using Nightmare APIs as a sample to do the automated page tests, which can help our continuous page performance test process on daily basis:

 var url = "http://www.yourhost.com/abc/def/";  
 var page_complete_idy = 'key_request_name'; //page indicator by resource name  
 var tag = 'ReviewPage';  
 var env_name = 'prod'; 

 const RENDER_TIME_MS = 2000;  

var Nightmare = require('nightmare'),
  nightmare = Nightmare({show: true, switches: {
    'ignore-certificate-errors': true
  }});

nightmare
  .goto(url)
  .wait(function(idy){
    var perfEntries = window.performance.getEntries();
    if (perfEntries.length > 20) {
      return perfEntries.some( function (item) {
        if (item.name.includes(idy)) {
          return true;
        }
      });
    } else {
      return false;
    }
  }, page_complete_idy)
  .evaluate(function(idy){
    var perfEntries = window.performance.getEntries();
    var perf_obj = perfEntries.find(function (item) {
      return item.name.includes(idy)
    });
    if (perf_obj) {
      return perf_obj.responseEnd.toFixed(1);
    } else {
      return 'undefined'
    }
  }, page_complete_idy)
  .end()
  .then( function (duration) {
    console.log(tag + ":" + duration);
  })