Get array of unique, 3rd party resources

filter-3p-resources.js

var firstPartyHostnamePattern = /^(?:.*)(?:nytimes\.com|nyt\.com|nyt\.net)$/;

// filter out 1st party resources
var thirdPartyResources = window.performance.getEntriesByType('resource').filter(function (entry){
  var url = new URL(entry.name);
  return !firstPartyHostnamePattern.test(url.hostname);
});

// reduce to unique host names
var thirdPartyHostnames = thirdPartyResources.map(function (entry){
  return new URL(entry.name).hostname;
}).reduce(function (prev, curr){
  if (prev.indexOf(curr) === -1) { prev.push(curr); }
  return prev;
}, []);

// generate map from host name to array of resources
var thirdPartyUrlsByHostname = thirdPartyHostnames.reduce(function (prev, curr){
  var resourcesByHost = {};
  resourcesByHost[curr] = thirdPartyResources.filter(function (resource){
    var resourceHostname = new URL(resource.name).hostname;
    return resourceHostname === curr;
  }).map(function (resource){
    return new URL(resource.name).pathname;
  });
  return Object.assign(prev, resourcesByHost);
}, {});

// calculate total 3p resources
var total3pResources = Object.keys(thirdPartyUrlsByHostname).reduce(function (prev, curr){
  return prev + thirdPartyUrlsByHostname[curr].length;
}, 0);

// calculate % of all resources that are 3p resources
var thirdPartyPercent = (total3pResources / window.performance.getEntriesByType('resource').length) * 100;