static compute()

in src/sdk/trace-metrics.ts [103:156]

• 39 lines of code
• 5 McCabe index (conditional complexity)

  static compute(trace: LHProcessedNavigation) {
    const traces: Array<TraceOutput> = [];
    const { timestamps, timings, lcpInvalidated } = trace;

    traces.push(this.buildMetric('navigationStart', timestamps.timeOrigin));
    traces.push(
      this.buildMetric('firstContentfulPaint', timestamps.firstContentfulPaint)
    );
    /**
     * lcpInvalidated - Denotes when all of the LCP events that comes from the
     * current trace are invalidated. Happens if the previous LCP candidates were
     * suppressed by another event coming later during the page load
     * More info - https://github.com/WICG/largest-contentful-paint/#the-last-candidate
     */
    !lcpInvalidated &&
      traces.push(
        this.buildMetric(
          'largestContentfulPaint',
          timestamps.largestContentfulPaint
        )
      );
    traces.push(
      this.buildMetric('domContentLoaded', timestamps.domContentLoaded)
    );
    traces.push(this.buildMetric('loadEvent', timestamps.load));

    /**
     * Lighthouse tracer extracts these metrics in milliseconds resolution,
     * we convert them to microseconds resolution to keep them in sync with
     * other timings
     */
    const millisToMicros = (value?: number) =>
      value ? value * 1000 : undefined;
    const keys = [
      'firstContentfulPaint',
      'largestContentfulPaint',
      'domContentLoaded',
      'load',
    ];
    const values = ['fcp', 'lcp', 'dcl', 'load'];
    const metrics = {};

    for (let i = 0; i < keys.length; i++) {
      const microSecs = millisToMicros(timings[keys[i]]);
      if (microSecs) {
        metrics[values[i]] = { us: microSecs };
      }
    }

    return {
      metrics,
      traces: traces.filter(b => Boolean(b)),
    };
  }