return; 
  prepend: function(node) {    if (this.first === null) {      this.append(node);    } else {      node.prev = this.last;      node.next = this.first;      this.first.prev = node;      this.last.next = node;      this.first = node;    }    this.length++;  },
3123	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/3123/5bb35ddb3516d7e68f3747d86540ffaa68de3fe3/linkedlist.js/clean/src/linkedlist.js