typeahead bootstrap 4 add multiple values

                                    function extractor(query) {
    var result = /([^,]+)$/.exec(query);
    if(result && result[1])
        return result[1].trim();
    return '';
}

$('.typeahead').typeahead({
    source: source,
    updater: function(item) {
        return this.$element.val().replace(/[^,]*$/,'')+item+',';
    },
    matcher: function (item) {
      var tquery = extractor(this.query);
      if(!tquery) return false;
      return ~item.toLowerCase().indexOf(tquery.toLowerCase())
    },
    highlighter: function (item) {
      var query = extractor(this.query).replace(/[\-\[\]{}()*+?.,\\\^$|#\s]/g, '\\$&')
      return item.replace(new RegExp('(' + query + ')', 'ig'), function ($1, match) {
        return '<strong>' + match + '</strong>'
      })
    }
});