This simple script converts a text string into a valid URL slug. It mixes jQuery with standard JavaScript, and can be easily adapted to pure JS.

<!-- Example input element -->
<input id="controlId" type="text" />

// Handles typing
$(document).ready(function () {
  // If the Title is specified, avoid overwrite
  if ($('#controlId').val().length === 0) {
    $('#controlId').on('keypress', function () {
      $('#controlId').val(slugify($('#controlId').val().toLowerCase()));
    });
  }
});

// Replacements
function slugify(text) {
  text = text.replace(/[^-a-zA-Z0-9,&\s]+/g, '');
  text = text.replace(/-/g, '_');
  text = text.replace(/\s/g, '-');
  return text;
}

Note (2025): For modern projects you may also want to normalize accents (é → e), trim repeated separators, and prefer input event instead of keypress. This post keeps the original 2010 logic.