speedline.js

/**
 * @license Copyright 2016 The Lighthouse Authors. 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';

import {makeComputedArtifact} from './computed-artifact.js';
import speedline from 'speedline-core';
import {LighthouseError} from '../lib/lh-error.js';
import ProcessedTrace from './processed-trace.js';

class Speedline {
  /**
   * @param {LH.Trace} trace
   * @param {LH.Artifacts.ComputedContext} context
   * @return {Promise<LH.Artifacts.Speedline>}
   */
  static async compute_(trace, context) {
    // speedline() may throw without a promise, so we resolve immediately
    // to get in a promise chain.
    return ProcessedTrace.request(trace, context).then(processedTrace => {
      // Use a shallow copy of traceEvents so speedline can sort as it pleases.
      // See https://github.com/GoogleChrome/lighthouse/issues/2333
      const traceEvents = trace.traceEvents.slice();
      // Force use of timeOrigin as reference point for speedline
      // See https://github.com/GoogleChrome/lighthouse/issues/2095
      const timeOrigin = processedTrace.timestamps.timeOrigin;
      return speedline(traceEvents, {
        timeOrigin,
        fastMode: true,
        include: 'speedIndex',
      });
    }).catch(err => {
      if (/No screenshots found in trace/.test(err.message)) {
        throw new LighthouseError(LighthouseError.errors.NO_SCREENSHOTS);
      }

      throw err;
    }).then(speedline => {
      if (speedline.frames.length === 0) {
        throw new LighthouseError(LighthouseError.errors.NO_SPEEDLINE_FRAMES);
      }

      if (speedline.speedIndex === 0) {
        throw new LighthouseError(LighthouseError.errors.SPEEDINDEX_OF_ZERO);
      }

      return speedline;
    });
  }
}

export default makeComputedArtifact(Speedline, null);