Vue项目如何根据图片url获取file对象并用axios上传

<script>
export default {
  data() {
    return {
	  ruleForm: {
        coverUrl: "",
        coverFile: ""
      },
    };
  },
  methods: {
    imgUrlToFile(url) {
      var self = this;
      var imgLink = url;
      var tempImage = new Image();
      //如果图片url是网络url，要加下一句代码
      tempImage.crossOrigin = "*";
      tempImage.onload = function() {
        var base64 = self.getBase64Image(tempImage);
        var imgblob = self.base64toBlob(base64);
        var filename = self.getFileName(self.ruleForm.coverUrl);
        self.ruleForm.coverFile = self.blobToFile(imgblob, filename);
      };
      tempImage.src = imgLink;
    },
    getBase64Image(img) {
      var canvas = document.createElement("canvas");
      canvas.width = img.width;
      canvas.height = img.height;
      var ctx = canvas.getContext("2d");
      ctx.drawImage(img, 0, 0, img.width, img.height);
      var ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase();
      var dataURL = canvas.toDataURL("image/" + ext);
      return dataURL;
    },
    base64toBlob(base64) {
      let arr = base64.split(","),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);
      while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
      }
      return new Blob([u8arr], { type: mime });
    },
    blobToFile(blob, filename) {
      // edge浏览器不支持new File对象，所以用以下方法兼容
      blob.lastModifiedDate = new Date();
      blob.name = filename;
      return blob;
    },
    getFileName(url) {
      // 获取到文件名
      let pos = url.lastIndexOf("/"); // 查找最后一个/的位置
      return url.substring(pos + 1); // 截取最后一个/位置到字符长度，也就是截取文件名
    }
  }
};
</script>

submitForm() {
    //...
    var filename = this.getFileName(this.ruleForm.coverUrl);
    params.append(
      "course_cover",
      this.ruleForm.coverFile,
      filename
    );
    //....
}

<input name="file" type="file" accept="image/png,image/gif,image/jpeg" @change="update"/>

import axios from 'axios'
// 添加请求头
update (e) {   // 上传照片
      var self = this
      let file = e.target.files[0]
      /* eslint-disable no-undef */
      let param = new FormData()  // 创建form对象
      param.append('file', file)  // 通过append向form对象添加数据
      param.append('chunk', '0') // 添加form表单中其他数据
      console.log(param.get('file')) // FormData私有类对象，访问不到，可以通过get判断值是否传进去
      let config = {
        headers: {'Content-Type': 'multipart/form-data'}
      }
     // 添加请求头
    axios.post('http://172.19.26.60:8081/rest/user/headurl', param, config)
        .then(response => {
          if (response.data.code === 0) {
            self.ImgUrl = response.data.data
          }
          console.log(response.data)
        })
    }