You can use a regular expression to check the file extension type, example below:

// name of file
var filename = "file.txt";

// use a regex to check file type
// | = "or" operator
// check for multiple file types
if(filename.match(/.txt|.doc|.pdf|.psd/)){
    alert('Only image & video files are available for preview')
} else {
 // execute my logic

}

if you want to check if filename match one of specific extensions, you can use the following function

const isExtensionMatch = (filename, matchedExtensions) => {
  const value = filename.split('.');

  let extension;
  if (value.length > 1) {
    extension = value[value.length - 1];
  }

  return new RegExp('^(' + matchedExtensions.join('|') + ')$').test(extension);
};

console.log(isExtensionMatch('filename.png', ['png', 'jpg'])); // true
console.log(isExtensionMatch('filename.sometext.png', ['png', 'jpg'])); // true
console.log(isExtensionMatch('filename.sometext.jpg', ['png', 'jpe?g'])); // true
console.log(isExtensionMatch('filename.sometext.jpeg', ['png', 'jpe?g'])); // true
console.log(isExtensionMatch('filename.sometext.jpeg', ['png', 'mp4'])); // false
console.log(isExtensionMatch('filename.sometext.jpeg.sometext', ['png', 'jpe?g'])); // false

Right now, during uploading file(s) all type of files are previewing. Although document type file is not previewing, it’s previewing like when an image source not found. However, I only want to preview the file(s) which are image & video. I don’t want to preview the document type files in my file preview section of HTML.