sitespeed.io/lib/support/statsHelpers.js

Analyze the web performance of your site

'use strict';

const Stats = require('fast-stats').Stats,
  get = require('lodash.get'),
  set = require('lodash.set');

function percentileName(percentile) {
  if (percentile === 0) {
    return 'min';
  } else if (percentile === 100) {
    return 'max';
  } else {
    return 'p' + String(percentile).replace('.', '_');
  }
}

function isFiniteNumber(n) {
  return typeof n === 'number' && isFinite(n);
}

module.exports = {
  /**
   * Create or update a fast-stats#Stats object in target at path.
   */
  pushStats(target, path, data) {
    if (!isFiniteNumber(data))
      throw new Error(`Tried to add ${data} to stats for path ${path}`);

    const stats = get(target, path, new Stats());
    stats.push(data);
    set(target, path, stats);
  },

  pushGroupStats(target, domainTarget, path, data) {
    this.pushStats(target, path, data);
    this.pushStats(domainTarget, path, data);
  },

  /**
   * Summarize stats and put result in target at path
   */
  setStatsSummary(target, path, stats) {
    set(target, path, this.summarizeStats(stats));
  },

  setStatsSummaryWithOptions(target, path, stats, options) {
    set(target, path, this.summarizeStats(stats, options));
  },

  summarizeStats(stats, options) {
    if (stats.length === 0) {
      return undefined;
    }

    options = options || {};
    let percentiles = options.percentiles || [0, 90, 100];
    let decimals = options.decimals || 0;
    if (stats.median() < 1 && stats.median() > 0) {
      decimals = 4;
    }

    let data = {
      median: parseFloat(stats.median().toFixed(decimals)),
      mean: parseFloat(stats.amean().toFixed(decimals))
    };
    percentiles.forEach(p => {
      let name = percentileName(p);
      const percentile = stats.percentile(p);
      if (Number.isFinite(percentile)) {
        data[name] = parseFloat(percentile.toFixed(decimals));
      } else {
        throw new Error(
          'Failed to calculate ' +
            name +
            ' for stats: ' +
            JSON.stringify(stats, null, 2)
        );
      }
    });
    if (options.includeSum) {
      data.sum = parseFloat(stats.Σ().toFixed(decimals));
    }

    return data;
  }
};