js通过正则表达式，判断文件类型

getFileType (url) {
      let pdfReg = /^.+(\.pdf)$/
      let txtReg = /^.+(\.txt)$/
      let wordReg = /^.+(\.doc|\.docx)$/
      let excelReg = /^.+(\.xls|\.xlsx)$/
      let jpgReg = /^.+(\.png|\.jpg|\.jpeg|\.bmp)$/
      if (pdfReg.test(url)) {
        return 'pdf'
      }
      if (txtReg.test(url)) {
        return 'txt'
      }
      if (wordReg.test(url)) {
        return 'word'
      }
      if (excelReg.test(url)) {
        return 'excel'
      }
      if (jpgReg.test(url)) {
        return 'picture'
      }
    }