# all files / lighthouse-core/audits/ critical-request-chains.js

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     /**
     * @license
     * Copyright 2016 Google Inc. All rights reserved.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    'use strict';

    const Audit = require('./audit');
    const Formatter = require('../formatters/formatter');

    class CriticalRequestChains extends Audit {
      /**
       * @return {!AuditMeta}
       */
      static get meta() {
        return {
          category: 'Performance',
          name: 'critical-request-chains',
          description: 'Critical Request Chains',
          optimalValue: 0,
          requiredArtifacts: ['CriticalRequestChains']
        };
      }

      /**
       * Audits the page to give a score for First Meaningful Paint.
       * @param {!Artifacts} artifacts The artifacts from the gather phase.
       * @return {!AuditResult} The score from the audit, ranging from 0-100.
       */
      static audit(artifacts) {
        let chainCount = 0;
        function walk(node, depth) {
          const children = Object.keys(node);

          // Since a leaf node indicates the end of a chain, we can inspect the number
          // of child nodes, and, if the count is zero, increment the count.
          if (children.length === 0) {
            chainCount++;
          }

          children.forEach(id => {
            const child = node[id];
            walk(child.children, depth + 1);
          }, '');
        }

        walk(artifacts.CriticalRequestChains, 0);

        return CriticalRequestChains.generateAuditResult({
          value: chainCount,
          optimalValue: this.meta.optimalValue,
          extendedInfo: {
            formatter: Formatter.SUPPORTED_FORMATS.CRITICAL_REQUEST_CHAINS,
            value: artifacts.CriticalRequestChains
          }
        });
      }
    }

    module.exports = CriticalRequestChains;