Pre-fill custom fields in Zendesk

prefill.js

jQuery(function($) {

  var customFieldParam = /^ticket\[fields\]\[(\d+)\]$/,
      urlParams = $.queryParameters(),
      k, match, fieldID;

  // for each URL parameter:
  for (k in urlParams) {
    if (urlParams.hasOwnProperty(k)) {
      // check whether it's a Zendesk custom field
      match = k.match(customFieldParam);
      if (match) {
        // pull out the ID:
        fieldID = match[1];
        // and set the value in the UI:
        $('#ticket_fields_' + fieldID).val(urlParams[k]);
      }
    }
  }

});