index.js

function getTicker(log) {
  log = log || Function.prototype

  var nativeNextTick = process.nextTick
  var ticking = false

  function nextTick() {
    if (!ticking) {
      ++nextTick._tick
      ticking = true
      nativeNextTick(function () {
        log(nextTick._tick)
        // Do not put this statement before the one above
        // That would cause `nextTick` calling itself forever
        ticking = false
      })
    }

    nativeNextTick.apply(null, arguments)
  }

  nextTick._tick = 0

  return nextTick
}

// Only for test
exports._nextTick = getTicker()

exports.polyfill = function (opts) {
  // already hacked
  if (process.nextTick._tick != null) return

  var env = process.env.NODE_DEBUG
  if (!env || !/\bnexttick\b/.test(env)) return

  opts = opts || {}

  var template = '---------- TICK %d ----------'
  if (opts.color) {
    template = '\x1b[32m' + template + '\x1b[0m'
  }

  var log = opts.log !== false && function (tick) {
    console.error(template, tick)
  }

  process.nextTick = getTicker(log)
}