js 截取后缀名

function getFileExtension(filename) {
  let parts = filename.split('.');
  if (parts.length > 1) {
    return parts.pop();
  }
  return '';
}

let filename = "example.txt";
console.log(getFileExtension(filename)); 

function getFileExtension(filename) {
  let index = filename.lastIndexOf('.');
  if (index !== -1 && index < filename.length - 1) {
    return filename.substring(index + 1);
  }
  return '';
}

let filename = "example.txt";
console.log(getFileExtension(filename)); 

function getFileExtension(filename) {
  if (!filename.includes('.') || filename.startsWith('.')) {
    return '';
  }
  let index = filename.lastIndexOf('.');
  return filename.substring(index + 1);
}