axios如何跨域请求（axios取消请求与避免重复请求）

// create an axios instance
const service = axios.create({
  baseURL: process.env.VUE_APP_BASE_API, // url = base url + request url
  withCredentials: true, // send cookies when cross-domain requests
  timeout: 500000, // request timeout
  transformRequest: [function(data) {
    // 对 data 进行任意转换处理
    return Qs.stringify({
      ...data
    },
    // 数组的转换
    { arrayFormat: 'brackets' })
  }]
})

// request interceptor
service.interceptors.request.use(
  config => {
    // do something before request is sent

    if (store.getters.token) {
      // let each request carry token
      // ['X-Token'] is a custom headers key
      // please modify it according to the actual situation
      config.headers['token'] = getToken()
    }
    return config
  },
  error => {
    // do something with request error
    console.log(error) // for debug
    return Promise.reject(error)
  }
)

export function remoteApi(data) {
  return request({
    url: '/api',
    method: 'post',
    data
  })
}

const CancelToken = axios.CancelToken;
const source = CancelToken.source();

axios.get('/user/12345', {
  cancelToken: source.token
}).catch(function(thrown) {
  if (axios.isCancel(thrown)) {
    console.log('Request canceled', thrown.message);
  } else {
     // 处理错误
  }
});

axios.post('/user/12345', {
  name: 'new name'
}, {
  cancelToken: source.token
})

// 取消请求（message 参数是可选的）
source.cancel('Operation canceled by the user.');

export function remoteApi(data, cancelToken) {
  return request({
    url: '/api',
    method: 'post',
    cancelToken,
    data
  })
}

// 组件方法内
this.cancelToken = CancelToken.source()
remoreApi(data, this.cancelToken).then(....).catch(....).finally(....)

// 组件方法内
this.cancelToken.cancel('取消下载')