function array_keys (input, search_value, argStrict) {
  // http://kevin.vanzonneveld.net
  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +      input by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   improved by: jd
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   input by: P
  // +   bugfixed by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: array_keys( {firstname: 'Kevin', surname: 'van Zonneveld'} );
  // *     returns 1: {0: 'firstname', 1: 'surname'}

  var search = typeof search_value !== 'undefined',
    tmp_arr = [],
    strict = !!argStrict,
    include = true,
    key = '';

  if (input && typeof input === 'object' && input.change_key_case) { // Duck-type check for our own array()-created PHPJS_Array
    return input.keys(search_value, argStrict);
  }

  for (key in input) {
    if (input.hasOwnProperty(key)) {
      include = true;
      if (search) {
        if (strict && input[key] !== search_value) {
          include = false;
        }
        else if (input[key] != search_value) {
          include = false;
        }
      }

      if (include) {
        tmp_arr[tmp_arr.length] = key;
      }
    }
  }

  return tmp_arr;
}

array_keys( {firstname: 'Kevin', surname: 'van Zonneveld'} );

{0: 'firstname', 1: 'surname'}