SOURCE

console.log(1)

setTimeout(() => {
  console.log(2)
})
new Promise((resolve, reject) => {
  console.log(3)
  setTimeout(() => {
    reject()
  }, 1)
}).then(() => {
  console.log(4)
}).catch(() => {
  console.log(5)
})
var $ajax = new XMLHttpRequest()
$ajax.open('get', 'http://yapi.demo.qunar.com/mock/5691/app')
$ajax.send(null)
$ajax.onreadystatechange = function() {
  if ($ajax.readyState == 4) {
    if ($ajax.status == 200) {
      console.log(6)
    }
  }
}