To split a file name into the name and extension, you can use the following function:

function splitFileName(fileName) {
  // Get the extension with a regular expression
  const ext = /(?:\.([^.]+))?$/.exec(fileName);
  // If there is no extension, return the filename with no extension
  if (ext[1] === undefined) return [fileName, ''];
  // Get the file name without extension
  const name = fileName.slice(0, -ext[0].length);
  // Return an array with name and extension
  return [name, ext[1]]
}

The above function works with the following filenames (outputs are displayed in the console):

splitFileName('filename.txt');  // ["filename", "txt"]
splitFileName('file.name.txt');  // ["file.name", "txt"]
splitFileName('filename');  // ["filename", ""]
splitFileName('file.name.with.dots.txt');  // ["file.name.with.dots", "txt"]
splitFileName('.htaccess');  // ["", "htaccess"]
splitFileName('');  // ["", ""]

Here is an online running code:

In Node.js, you can use path.parse():

var path = require('path');

var fileName = "filename.txt";
console.log(path.parse(fileName).name); // filename
console.log(path.parse(fileName).ext); // txt