# all files / src/audits/performance/ user-timings.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');
    const TimelineModel = require('../../lib/traces/devtools-timeline-model');

    const FAILURE_MESSAGE = 'Trace data not found.';

    class UserTimings extends Audit {
      /**
       * @override
       */
      static get meta() {
        return {
          category: 'Performance',
          name: 'user-timings',
          description: 'User Timing measures',
          requiredArtifacts: ['traceContents']
        };
      }

      /**
       * @param {!Artifacts} artifacts
       * @return {!AuditResult}
       */
      static audit(artifacts) {
        if (!artifacts.traceContents || !Array.isArray(artifacts.traceContents)) {
          return UserTimings.generateAuditResult({
            value: -1,
            debugString: FAILURE_MESSAGE
          });
        }

        let timingsCount = 0;

        // Fetch blink.user_timing events from the tracing data
        const timelineModel = new TimelineModel(artifacts.traceContents);
        const modeledTraceData = timelineModel.timelineModel();
        const key = [...modeledTraceData.mainThreadAsyncEvents().keys()].find(
          key => key.title === 'User Timing'
        );
        let userTimings = modeledTraceData.mainThreadAsyncEvents().get(key);

        // Reduce events to record only useful information
        if (typeof userTimings !== 'undefined') {
          timingsCount = userTimings.length;
          userTimings = userTimings.map(ut => {
            return {
              name: ut.name,
              startTime: ut.startTime,
              endTime: ut.endTime,
              duration: ut.duration.toFixed(2) + 'ms',
              args: ut.args
            };
          });
        }

        return UserTimings.generateAuditResult({
          value: timingsCount,
          extendedInfo: {
            formatter: Formatter.SUPPORTED_FORMATS.USER_TIMINGS,
            /* Pass empty array rather than undefined */
            value: userTimings || []
          }
        });
      }
    }

    module.exports = UserTimings;