coach-core/lib/har/performance/fewRequestsPerDomain.js

Core package for the Coach.

import * as util from '../util.js';

export default {
  id: 'fewRequestsPerDomain',
  title: 'Avoid too many requests per domain [HTTP/1]',
  description:
    'Browsers have a limit on how many concurrent requests they can do per domain when using HTTP/1. When you hit the limit, the browser will wait before it can download more assets on that domain. So avoid having too many requests per domain.',
  weight: 5,
  severity: 'info',
  tags: ['performance', 'HTTP/1'],
  processPage: function (page) {
    let limit = 30;
    if (util.isHTTP2(page)) {
      return {
        score: 100,
        offending: [],
        advice:
          'There are almost no limits on HTTP/2 connections with the number of requests, but that is not completely true. It depends on how they are downloaded. Please check your HAR file, does it look OK?'
      };
    } else if (util.isHTTP3(page)) {
      return {
        score: 100,
        offending: [],
        advice:
          'HTTP/3 connections is new and there are no best practices at the moment.  Please check your HAR file, does it look OK?'
      };
    }

    const infoPerDomain = page.domains;
    let offending = [];
    let domainAndRequests = {};
    let score = 100;
    let advice = '';
    Object.keys(infoPerDomain).reduce((result, domain) => {
      if (infoPerDomain[domain].requests > limit) {
        score -= 10;
        offending.push(domain);
        domainAndRequests[domain] = infoPerDomain[domain].requests;
      }
      return domainAndRequests;
    });

    if (score < 100) {
      advice =
        'The page has ' +
        util.plural(offending.length, 'domain') +
        ' that serves more than ' +
        limit +
        ' requests. ';

      for (const domain of Object.keys(domainAndRequests)) {
        advice +=
          domain +
          ' got ' +
          util.plural(domainAndRequests[domain], 'request') +
          '. ';
      }
      advice += 'Improve performance by sharding those or move to HTTP/2.';
    }

    return {
      score: Math.max(0, score),
      offending: offending,
      advice: advice
    };
  }
};