metric.js

import warning from 'warning'

const times = new Map()

const implementations = {
  mark: {
    start: name => {
      times.set(name, performance.now())
      performance.mark(`metric_${name}_start`)
    },
    end: name => {
      const endMark = `metric_${name}_end`
      performance.mark(endMark)
      const startMark = `metric_${name}_start`
      performance.measure(name, startMark, endMark)
      const duration = performance.getEntriesByName(name)[0].duration
      return duration
    },
  },
  now: {
    start: name => {
      times.set(name, performance.now())
    },
    end: name => {
      const time = times.get(name)
      const duration = performance.now() - time
      return duration
    },
  },
  hrtime: {
    start: name => {
      // https://nodejs.org/api/process.html#process_process_hrtime_time
      times.set(name, process.hrtime())
    },
    end: name => {
      const time = times.get(name)
      const durations = process.hrtime(time)
      return durations[0] * 1e3 + durations[1] / 1e6
    },
  },
}

let getImplementationCache

function getImplementation() {
  if (getImplementationCache) {
    return getImplementationCache
  }

  if (typeof performance !== 'undefined' && performance.mark) {
    getImplementationCache = implementations.mark
  } else if (typeof performance !== 'undefined' && performance.now) {
    getImplementationCache = implementations.now
  } else if (process.hrtime) {
    getImplementationCache = implementations.hrtime
  } else {
    throw new Error('No performance API available')
  }

  return getImplementationCache
}

class Metric {
  /**
   * Call to begin a measurement.
   */
  static start(name) {
    warning(!times.get(name), 'Recording already started')
    getImplementation().start(name)
  }

  /**
   * Returns the duration of the timing metric. The unit is milliseconds.
   * @type {number}
   */
  static end(name) {
    if (!times.get(name)) {
      throw new Error(`No such name '${name}' for metric`)
    }

    const duration = getImplementation().end(name)
    times.delete(name)
    return duration
  }

  name = ''

  /**
   * @param {string} name A name for the metric.
   */
  constructor(name) {
    if (!name) {
      throw new Error('Please provide a metric name')
    }

    this.name = name
  }

  /**
   * Call to begin a measurement.
   */
  start(name) {
    if (name) {
      throw new Error('The name argument is not supported')
    }

    Metric.start(this.name)
  }

  /**
   * Returns the duration of the timing metric. The unit is milliseconds.
   * @type {number}
   */
  end(name) {
    if (name) {
      throw new Error('The name argument is not supported')
    }

    return Metric.end(this.name)
  }
}

export default Metric