首先，因为我这边项目是迭代的，只需要添加一个压缩功能，所以我这边是从获取到file之后开始写的。

1.前端：

<el-upload action="/FileUpload" :http-request="uploadSectionFile" :show-file-list="false" style="display:inline-block" :disabled="AttachmentCategoryID==0" v-if="CanEdit">
    	 <el-button type="primary" :disabled="AttachmentCategoryID==0">附件上传</el-button>
      	</el-upload>

  2、return{}里定义

	return{
  		headerImage:,
		 picValue:,
  }

 3.上传前压缩的方法

	uploadSectionFile(f) { //	附件上传
			let self = this;
			let Orientation;
			let ndata;

			if(f.file.size<=1* 1024* 1024){
			//判断图片是否大于1M,是就直接上传
			ndata=f.file;
            self.postImg(ndata);
			}else{
				//反之压缩图片
			   let reader = new FileReader();
				// 将图片2将转成 base64 格式
				reader.readAsDataURL(f.file);
				console.log(reader)
				// 读取成功后的回调
				reader.onloadend = function () {
				let result = this.result;
				let img = new Image();
				img.src = result;
               img.onload = function () {
                let data = self.compress(img,Orientation);
                self.headerImage = data;
				ndata=  self.compress(img,Orientation);
			  
				//BASE64转图片
				var arr = ndata.split(','), mime = arr[0].match(/:(.*?);/)[1],
				bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
				while(n--){
				u8arr[n] = bstr.charCodeAt(n);
				}
			   ndata=new File([u8arr],f.file.name, {type:mime})
				self.postImg(ndata);
		
            }
          } 
       }
        },async postImg (ndata) {
			let param = new FormData(); //创建form对象
            param.append('file', ndata); //通过append向form对象添加数据
            let config = {
                headers: {
                    'Content-Type': 'multipart/form-data'
                }
            }
            try {
                const response = await FileUpload(param, config)  //此处写接口对应的vue方法
			

                if (response.Code == 200) {
                    this.handleFileUploadSuccess(response.Data)
                }
            } catch (error) {
                console.log(error)}
      },
    compress(img,Orientation) {
      let canvas = document.createElement("canvas");
      let ctx = canvas.getContext('2d');
        //瓦片canvas
      let tCanvas = document.createElement("canvas");
      let tctx = tCanvas.getContext("2d");
      let initSize = img.src.length;
      let width = img.width;
      let height = img.height;
      //如果图片大于四百万像素，计算压缩比并将大小压至400万以下
      let ratio;
      if ((ratio = width * height / 4000000) > 1) {
        console.log("大于400万像素")
        ratio = Math.sqrt(ratio);
        width /= ratio;
        height /= ratio;
      } else {
        ratio = 1;
      }
      canvas.width = width;
      canvas.height = height;
  // 		铺底色
      	ctx.fillStyle = "#fff";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      //如果图片像素大于100万则使用瓦片绘制
      let count;
      if ((count = width * height / 1000000) > 1) {
        console.log("超过100W像素");
        count = ~~(Math.sqrt(count) + 1); //计算要分成多少块瓦片
  //            计算每块瓦片的宽和高
        let nw = ~~(width / count);
        let nh = ~~(height / count);
        tCanvas.width = nw;
        tCanvas.height = nh;
        for (let i = 0; i < count; i++) {
          for (let j = 0; j < count; j++) {
            tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
            ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
          }
        }
      } else {
        ctx.drawImage(img, 0, 0, width, height);
      }
      //修复ios上传图片的时候 被旋转的问题
      if(Orientation != "" && Orientation != 1){
        switch(Orientation){
          case 6://需要顺时针（向左）90度旋转
              this.rotateImg(img,'left',canvas);
              break;
          case 8://需要逆时针（向右）90度旋转
              this.rotateImg(img,'right',canvas);
              break;
          case 3://需要180度旋转
              this.rotateImg(img,'right',canvas);//转两次
              this.rotateImg(img,'right',canvas);
              break;
        }
      }
      //进行最小压缩
      let ndata = canvas.toDataURL('image/jpeg', 0.1);
	  
      console.log('压缩前：' + initSize);
      console.log('压缩后：' + ndata.length);
	  console.log("ndata:"+ndata)
	  
      console.log('压缩率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
      tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
	 

      return ndata;
    }`