javascript get file extension

var ext =  fileName.split('.').pop();

var ext = fileName.substr(fileName.lastIndexOf('.') + 1);

// Use the lastIndexOf method to find the last period in the string, and get the part of the string after that:

var ext = fileName.substr(fileName.lastIndexOf('.') + 1);

function getFileNameWithExt(event) {

  if (!event || !event.target || !event.target.files || event.target.files.length === 0) {
    return;
  }

  const name = event.target.files[0].name;
  const lastDot = name.lastIndexOf('.');

  const fileName = name.substring(0, lastDot);
  const ext = name.substring(lastDot + 1);

  outputfile.value = fileName;
  extension.value = ext;
  
}