element 上传图片转base64

HTML

<el-upload
  class="avatar-uploader"
  action=""
  :show-file-list="false"
  :on-change="getFile"
  :limit="1"
  list-type="picture"
  :auto-upload="false"
  >
  <img v-if="imageUrl" :src="imageUrl" class="avatar">
  <i v-else class="el-icon-plus avatar-uploader-icon"></i>
</el-upload>

JS

getFile (file, fileList) {
  this.getBase64(file.raw).then(res => {
    this.imageUrl = res
    console.log(res)
  })
},
getBase64 (file) {
  return new Promise(function (resolve, reject) {
    let reader = new FileReader()
    let imgResult = ''
    reader.readAsDataURL(file)
    reader.onload = function () {
      imgResult = reader.result
    }
    reader.onerror = function (error) {
      reject(error)
    }
    reader.onloadend = function () {
      resolve(imgResult)
    }
  })
}