browser.js

var scheduler = require('nanoscheduler')()
var assert = require('assert')

var perf
nanotiming.disabled = true
try {
  perf = window.performance
  nanotiming.disabled = window.localStorage.DISABLE_NANOTIMING === 'true' || !perf.mark
} catch (e) { }

module.exports = nanotiming

function nanotiming (name) {
  assert.equal(typeof name, 'string', 'nanotiming: name should be type string')

  if (nanotiming.disabled) return noop

  var uuid = (perf.now() * 10000).toFixed() % Number.MAX_SAFE_INTEGER
  var startName = 'start-' + uuid + '-' + name
  perf.mark(startName)

  function end (cb) {
    var endName = 'end-' + uuid + '-' + name
    perf.mark(endName)

    scheduler.push(function () {
      var err = null
      try {
        var measureName = name + ' [' + uuid + ']'
        perf.measure(measureName, startName, endName)
        perf.clearMarks(startName)
        perf.clearMarks(endName)
      } catch (e) { err = e }
      if (cb) cb(err, name)
    })
  }

  end.uuid = uuid
  return end
}

function noop (cb) {
  if (cb) {
    scheduler.push(function () {
      cb(new Error('nanotiming: performance API unavailable'))
    })
  }
}