ant-design-vue/components/upload/demo/transform-file.vue

<docs>
---
order: 10
title:
  zh-CN: 上传前转换文件
  en-US: Transform file before request
---

## zh-CN

使用 `beforeUpload` 转换上传的文件（例如添加水印）。

## en-US

Use `beforeUpload` for transform file before request such as add a watermark.
</docs>

<template>
  <div>
    <a-upload
      v-model:file-list="fileList"
      action="https://www.mocky.io/v2/5cc8019d300000980a055e76"
      :before-upload="beforeUpload"
    >
      <a-button>
        <upload-outlined></upload-outlined>
        Upload
      </a-button>
    </a-upload>
  </div>
</template>
<script lang="ts">
import { UploadOutlined } from '@ant-design/icons-vue';
import { defineComponent, ref } from 'vue';
import type { UploadProps } from 'ant-design-vue';

export default defineComponent({
  components: {
    UploadOutlined,
  },
  setup() {
    const beforeUpload: UploadProps['beforeUpload'] = file => {
      return new Promise(resolve => {
        const reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload = () => {
          const img: HTMLImageElement = document.createElement('img');
          img.src = reader.result as string;
          img.onload = () => {
            const canvas = document.createElement('canvas');
            canvas.width = img.naturalWidth;
            canvas.height = img.naturalHeight;
            const ctx = canvas.getContext('2d');
            ctx.drawImage(img, 0, 0);
            ctx.fillStyle = 'red';
            ctx.textBaseline = 'middle';
            ctx.font = '33px Arial';
            ctx.fillText('Ant Design Vue', 20, 20);
            canvas.toBlob(resolve);
          };
        };
      });
    };
    return {
      beforeUpload,
      fileList: ref([]),
    };
  },
});
</script>