大致步骤

• 1 图片分块
• 2 分块的图片 用formdata 保存在发后台

代码实现

   <template>
  <el-upload
    class="upload-demo"
    action="00"
    :on-preview="handlePreview"
    :on-remove="handleRemove"
    :before-remove="beforeRemove"
    :on-change = "onchangeHandle"
    multiple
    :limit="3"
    :on-exceed="handleExceed"
    :file-list="fileList"
    :auto-upload="false"
  >
    <el-button size="small" type="primary">Click to upload</el-button>
    <template #tip>
      <div class="el-upload__tip">
        jpg/png files with a size less than 500kb
      </div>
    </template>
  </el-upload>
  <el-progress :percentage="obj.currentLoading" :format="format" />
</template>

<script>
// https://www.jianshu.com/p/08524828f84b
// https://zhuanlan.zhihu.com/p/68271019
// 步骤简述 1图片分割 2formdata 保存数据上传后台  
import {defineComponent, reactive} from 'vue'
import { ElMessage,ElMessageBox } from 'element-plus'
export default defineComponent({
  name: 'HelloWorld',
  props: {
    msg: String
  },
  setup () {
    const fileList = reactive([])
    const obj = reactive({
      currentLoading: 0,
      current: 0
    })
    function handleRemove(file, fileList) {
        console.log(file, fileList)
    }
    function handlePreview(file) {
        console.log(file)
    }
    function handleExceed() {
        ElMessage(
        `www`
        )
    }
    function beforeRemove() {
        ElMessage(`Cancel the transfert of ?`)
    }
    const sliceImg =  (file, piece = 1024 * 1024 * 1) => { // 分割图片
      let totalSize = file.size; // 文件总大小
      let start = 0; // 每次上传的开始字节
      let end = start + piece; // 每次上传的结尾字节
      let chunks = []
      while (start < totalSize) {
        // 根据长度截取每次需要上传的数据
        // File对象继承自Blob对象，因此包含slice方法
        let blob = file.raw.slice(start, end); 
        chunks.push(blob)
        start = end;
        end = start + piece;
      }
      return chunks
    }
    const onchangeHandle = (file, fileList) => {
      console.log(file, fileList)
      let imgData = sliceImg(file)
      let loading = Math.floor(100/imgData.length) // 进度条每次的进度
      let time = imgData.length // 总共要发几次请求
      saveImg(imgData, loading, time, obj)
    }
    const saveImg = (arr, loading, time, obj) => {
      const formData = new FormData()
      const key = 'chunk' + obj.current
      formData.append('chunk', arr[obj.current])
      formData.append('filename', key)
      // 请求接口去
      setTimeout(() => {
        obj.current++
        obj.currentLoading = loading *obj.current
        if (obj.current < time) {
          saveImg(arr, loading, time, obj)
        } else {
          obj.currentLoading = 100
          ElMessageBox.alert('上传成功', '提示', {
            confirmButtonText: '确定',
            callback: () => {
              console.log('成')
            },
          })
        }
      }, 2000)
    }
    return {
        handleRemove,
        handlePreview,
        handleExceed,
        beforeRemove,
        fileList,
        onchangeHandle,
        obj
    }
  }
})
</script>

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
h3 {
  margin: 40px 0 0;
}
ul {
  list-style-type: none;
  padding: 0;
}
li {
  display: inline-block;
  margin: 0 10px;
}
a {
  color: #42b983;
}
</style>