Elemennt文件上传el-upload设置上传文件图片格式限制

beforeAvatarUploadPdf (file) {
        var testmsg = file.name.substring(file.name.lastIndexOf('.') + 1)
        const extension = testmsg === 'jpg'
        const extension2 = testmsg === 'png'
        const extension4 = testmsg === 'jpeg'
        if (!extension && !extension2) {
          this.$message({
            message: '上传文件只能是 jpg, jpeg, png格式!',
            type: 'warning'
          })
          return false
        }
        return extension || extension2 || extension4
      }