モバイル端末Vue+VANtのUploaderはアップロード、圧縮、回転画像機能を実現します。

 <van-uploader :after-read="onRead" accept="image/*">
    <img src="./icon_input_add.png" />
 </van-uploader>

data() {
    return {
      files: {
        name: "",
        type: ""
      },
      headerImage: null,
      picValue: null,
      upImgUrl,
    }
  },
  //          
  async onRead(file) {
      // console.log(file);
      // console.log(file.file);
      this.files.name = file.file.name; //      
      this.files.type = file.file.type; //     
      this.picValue = file.file; //    
      this.imgPreview(this.picValue);
    },
    //     
    imgPreview(file) {
      let self = this;
      let Orientation;
      //         ，            
      Exif.getData(file, function () {
        Orientation = Exif.getTag(this, "Orientation");
      });
      //       FileReader
      if (!file || !window.FileReader) return;
      if (/^image/.test(file.type)) {
        //     reader
        let reader = new FileReader();
        //    2    base64   
        reader.readAsDataURL(file);
        //         
        reader.onloadend = function () {
          // console.log(this.result);
          let result = this.result;
          let img = new Image();
          img.src = result;
          //        500K,      ，      
          if (this.result.length <= 500 * 1024) {
            self.headerImage = this.result;
            self.postImg();
          } else {
            img.onload = function () {
              let data = self.compress(img, Orientation);
              self.headerImage = data;
              self.postImg();
            };
          }
        };
      }
    },
    //     
    compress(img, Orientation) {
      let canvas = document.createElement("canvas");
      let ctx = canvas.getContext("2d");
      //  canvas
      let tCanvas = document.createElement("canvas");
      let tctx = tCanvas.getContext("2d");
      // let initSize = img.src.length;
      let width = img.width;
      let height = img.height;
      //           ，           400   
      let ratio;
      if ((ratio = (width * height) / 4000000) > 1) {
        // console.log("  400   ");
        ratio = Math.sqrt(ratio);
        width /= ratio;
        height /= ratio;
      } else {
        ratio = 1;
      }
      canvas.width = width;
      canvas.height = height;
      //       
      ctx.fillStyle = "#fff";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      //        100        
      let count;
      if ((count = (width * height) / 1000000) > 1) {
        // console.log("  100W  ");
        count = ~~(Math.sqrt(count) + 1); //          
        //                
        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);
      }
      //  ios              
      if (Orientation != "" && Orientation != 1) {
        switch (Orientation) {
          case 6: //     （  ）90   
            this.rotateImg(img, "left", canvas);
            break;
          case 8: //     （  ）90   
            this.rotateImg(img, "right", canvas);
            break;
          case 3: //  180   
            this.rotateImg(img, "right", canvas); //   
            this.rotateImg(img, "right", canvas);
            break;
        }
      }
      //      
      let ndata = canvas.toDataURL("image/jpeg", 0.1);
      tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
      return ndata;
    },
    //     
    rotateImg(img, direction, canvas) {
      //         ，    4       
      const min_step = 0;
      const max_step = 3;
      if (img == null) return;
      //img         img       ，     
      let height = img.height;
      let width = img.width;
      let step = 2;
      if (step == null) {
        step = min_step;
      }
      if (direction == "right") {
        step++;
        //      ，      
        step > max_step && (step = min_step);
      } else {
        step--;
        step < min_step && (step = max_step);
      }
      //           
      let degree = (step * 90 * Math.PI) / 180;
      let ctx = canvas.getContext("2d");
      switch (step) {
        case 0:
          canvas.width = width;
          canvas.height = height;
          ctx.drawImage(img, 0, 0);
          break;
        case 1:
          canvas.width = height;
          canvas.height = width;
          ctx.rotate(degree);
          ctx.drawImage(img, 0, -height);
          break;
        case 2:
          canvas.width = width;
          canvas.height = height;
          ctx.rotate(degree);
          ctx.drawImage(img, -width, -height);
          break;
        case 3:
          canvas.width = height;
          canvas.height = width;
          ctx.rotate(degree);
          ctx.drawImage(img, -width, 0);
          break;
      }
    },
    // base64     
    dataURLtoFile(dataurl) {
      var arr = dataurl.split(","),
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);
      while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
      }
      return new File([u8arr], this.files.name, {
        type: this.files.type
      });
    },
    //      
    async postImg() {
      let file = this.dataURLtoFile(this.headerImage);
      let formData = new window.FormData();
      formData.append("file", file);
      toast_loding(this, "     ・・・");
      try {
        let res = await util.ajax.post(this.upImgUrl, formData, {
          headers: {
            "Content-Type": "multipart/form-data"
          }
        });
      } catch (e) {
        console.log(e);
      }
    }