javascript - 如何以 Angular 获得图像的扩展？

Question

这里我使用下面的代码检查图像扩展。 imageName.split(".").pop() 使用 split 和 pop 我得到了图像扩展名，但在此之后我必须检查此扩展名是否与此匹配我必须检查多个或条件，所以代码的制作过程很慢，所以是否有可能减少代码并减少 OR 条件。

例。如果 jpEg extension image 那一次只有一个条件 (extn == jpeg) 是 check all type small,capital extension('jpeg','Jpeg','jPeg','jpEg','jpeG','JPeg','JpEg','JpeG','jPEg','jPeG','jpEG','jPEG ','JPeG','JPEg','JpEG','JPEG') 和 make less or 条件

previewFiles(imageName){
 console.log(imagename);  // 125.jpEg

 var extn = imageName.split(".").pop();

   console.log(extn);  // jpEg

  if((extn == 'pdf') || (extn == 'PDF') || (extn == 'pdF') || (extn == 'pDf') ||
     (extn == 'pDF') || (extn == 'PDf') || (extn == 'PdF') || (extn == 'Pdf') ||
     (extn == 'jpg') || (extn == 'JPG') || (extn == 'jpG') || (extn == 'jPg') ||
     (extn == 'jPG') || (extn == 'JPg') || (extn == 'JpG') || (extn == 'Jpg') ||
     (extn == 'gif') || (extn == 'GIF') || (extn == 'giF') || (extn == 'gIf') ||
     (extn == 'gIF') || (extn == 'GIf') || (extn == 'GiF') || (extn == 'Gif') ||
     (extn == 'png') || (extn == 'PNG') || (extn == 'pnG') || (extn == 'pNg') ||
     (extn == 'pNG') || (extn == 'PNg') || (extn == 'PnG') || (extn == 'Png') ||
     (extn == 'tif') || (extn == 'TIF') || (extn == 'tiF') || (extn == 'tIf') ||
     (extn == 'tIF') || (extn == 'TIf') || (extn == 'TiF') || (extn == 'Tif') ||
     (extn == 'jpeg') || (extn == 'Jpeg') || (extn == 'jPeg') || (extn == 'jpEg') ||
     (extn == 'jpeG') || (extn == 'JPeg') || (extn == 'JpEg') || (extn == 'JpeG') ||
     (extn == 'jPEg') || (extn == 'jPeG' ) || (extn == 'jpEG' ) || (extn == 'jPEG' ) ||
     (extn == 'JPeG' ) || (extn == 'JPEg') || (extn == 'JpEG') || (extn == 'JPEG') ||
     (extn == 'tiff') || (extn == 'Tiff' ) || (extn == 'tIff') || (extn == 'tiFf' ) ||
    (extn == 'tifF') || (extn == 'TIff') || (extn == 'TiFf') || (extn == 'TifF') ||
     (extn == 'tIFf') || (extn == 'tIfF') || (extn == 'tiFF') || (extn == 'tIFF') ||
     (extn == 'TIfF') || (extn == 'TIFf') || (extn == 'TiFF') || (extn == 'TIFF')){
      console.log("extension of image is matched");    
   }else{
      console.log("extension of image is not matched");
   }
}

Answer 1

您可以使用使用交替的正则表达式和 /i 进行不区分大小写的比较或使用 toLowerCase 进行字符串比较:

let extn = "TIFf";
const regex = /(?:pdf|jpeg|jpg|tiff?|gif|png)/i;
if (regex.test(extn)) {
  console.log(extn);
}

let valid = [
  "pdf", "tif", "tiff", "jpg", "jpeg", "gif", "png"
];

if (valid.includes(extn.toLowerCase())) {
  console.log(extn);
}