phpjs/functions/filesystem/dirname.js

php.js offers community built php functions in javascript

function dirname(path) {
  //  discuss at: http://phpjs.org/functions/dirname/
  // original by: Ozh
  // improved by: XoraX (http://www.xorax.info)
  //   example 1: dirname('/etc/passwd');
  //   returns 1: '/etc'
  //   example 2: dirname('c:/Temp/x');
  //   returns 2: 'c:/Temp'
  //   example 3: dirname('/dir/test/');
  //   returns 3: '/dir'

  return path.replace(/\\/g, '/')
    .replace(/\/[^\/]*\/?$/, '');
}