includes(value) {
    let current = this.head;
    while (current !== null) {
      if (current.data === value) {
        return true;
      }
      current = current.next;
    }
    return false;
  }
// test for existance of a node
test for existance of a node
test for existance of a node
includes(value) {
    let current = this.head;
    while (current !== null) {
      if (current.data === value) {
        return true;
      }
      current = current.next;
    }
    return false;
  }
includes ( value ) { let current = this . head ; while ( current !== null ) { if ( current . data === value ) { return true ; } current = current . next ; } return false ; }
test for existance of a node
test for existance of a node