vant上传图片时压缩图片

afterRead(file){
        console.log(file,'0000')
        this.face = [];
        let canvas = document.createElement('canvas') // 创建Canvas对象(画布)
        let context = canvas.getContext('2d')
        let img = new Image()
        img.src = file.content // 指定图片的DataURL(图片的base64编码数据)
        img.onload = () => {
          canvas.width = img.width/10
          canvas.height = img.height/10
          context.drawImage(img, 0, 0, img.width/10, img.height/10)
          file.content = canvas.toDataURL(file.file.type, 0.92) // 0.92为默认压缩质量
          console.log(file,file.content,'4444444')
          let files = this.dataURLtoFile(file.content, file.file.name)
          console.log(files,'33333')
          this.uploadToqiniu(files,this.face);
        }
      },

dataURLtoFile (dataurl, filename) { // 将base64转换为file文件
        let arr = dataurl.split(',')
        let mime = arr[0].match(/:(.*?);/)[1]
        let bstr = atob(arr[1])
        let n = bstr.length
        let u8arr = new Uint8Array(n)
        while (n--) {
          u8arr[n] = bstr.charCodeAt(n)
        }
        return new File([u8arr], filename, {type: mime})
      },