I don't know what is wrong with the callback in the last line in vue2. The webpage runs well but has red error showing "Uncaught (in promise) TypeError: callback is not a function at eval (index.js?74ed:313:1)"

const login = (force, callback) => {
  var token = localStorage.getItem('token')
  if (!token) {
    return
  }
  if (!force) {
    force = 0
  }
  let browser = Global.config.browser === 'qt' ? 10 : 11
  app.post('/active', {
    'domain': domain,
  })
    .then(response => {
      if (response.data.error === 0) {
        
        var back = 0
        callback(back)
      } else {
        back = 1
        callback(back)
      }
    })
    .catch(error => {
      if (error.response) {
        var back = 3
      } else {
        back = 2
      }
      callback(back)
    })
}