element upload 上传文件之前的格式校验

uploadBeforeUploadHandle(file) {
      this.flag = false
      var extName = file.name.substring(file.name.lastIndexOf('.')).toLowerCase()
      var AllUpExt = '.jpg|.jpeg|.png|.doc|.docx|.xls|.xlsx|.ppt|.mp4|.pdf|.dwt|.dwg|.dws|.dxf|'
      const isLt2M = file.size / 1024 / 1024 < 5
      if (AllUpExt.indexOf(extName + '|') === -1) {
        this.$message.error('文件格式不正确!')
        return false
      }
      if(!isLt2M) {
        this.$message.error('上传文件大小不能超过5MB!')
        return false
				}
    },