var xhr = new XMLHttpRequest()

// 配置的代理，解决跨域问题

xhr.open('GET', url.replace('http://xxx.com', '/img'), true)

xhr.responseType = 'blob'

xhr.onload = function () {

  if (xhr.status === 200) {

    var reader = new FileReader()

    reader.readAsDataURL(xhr.response)

    reader.onloadend = function () {

      var base64data = reader.result.replace(/^data:image\/(png|jpg);base64,/, "")

    }

  }

}

xhr.send()