var assert = require('assert')

module.exports = documentReady

function documentReady (callback) {
  assert.notEqual(typeof document, 'undefined', 'document-ready only runs in the browser')

  var state = document.readyState
  if (state === 'complete' || state === 'interactive') {
    return setTimeout(callback, 0)
  }

  document.addEventListener('DOMContentLoaded', function onLoad () {
    callback()
  })
}