Convert a string into a standard page slug by removing non-alpha/numeric.

slugify.js

/**
 * Convert a string into a standard slug by replacing all non alpha numeric characters
 * with the passed separator or a hyphen. Also removing duplicate separators, and
 * separators at the beginning or end of a slug.
 *
 * @param {String} tring The string slugify.
 * @param {String} eparator The character or string to substitute.
 * @returns {String|Undefined} The original, slugified, or undefined string.
 */
function slugify(string, separator) {
  if (!string) {
    return undefined;
  }
  if (typeof string !== 'string') {
    return string;
  }
  var sep = typeof separator === 'string' ? separator : '-';
  var regEx = new RegExp('[^a-z0-9]+', 'g');
  var str = string.toLowerCase();
  var slug = str.replace(regEx, sep);

  return slug;
}