MiniTreeWalker の作りかけ

まだ、修正中ですが、アドバイスお願いします^^;

var Filter_ACCEPT = 1;
var Filter_REJECT = 2;
var Filter_SKIP = 3;


var createMiniTreeWalker = function ( root/* node */, filter/* Function */  ) {
  if( !root ) return null;
  if( 'function' !== typeof filter )
    filter = function ( node ) { return node; }; // defaultFunction
    
  return new MiniTreeWalker( root, filter );
};


var MiniTreeWalker = function ( root, filter ) {

  //現在のノードの深さ
  var depth = 0;


  //現在の基準のノード
  this.currentNode = root; //初期値？
  

  //先祖探し
  this.parentNode = function ( ) {
    var n = this.currentNode;
    var r;
    
    while( n = n.parentNode && 0 < depth-- ) {
      r = filter( n );
      if( 1 == r ) return this.currentNode = n;
      if( 2 == r ) return null;
//    if( 3 == r );
    }
    return null;
  };

  
  //最初の子
  this.firstChild = function ( ) {
    var n = this.currentNode.firstChild;
    var r;
    
    while( n ) {
      r = filter( n );
      if( 1 == r ) return ( depth++, this.currentNode = n );
      if( 2 == r ) null;
//    if( 3 == r );
      n = n.nextSibling;
    }
    return null;
  };
  
  
  //最後の子
  this.lastChild = function ( ) {
    var n, r;
    
    if( this.currentNode.hasChildNodes() ) {
      n = this.currentNode.lastChild, depth++;
      do {
        r = filter( n );
        if( 1 == r ) return ( this.currentNode = n );
        if( 2 == r ) return null;
//      if( 3 == r );
      }
      while( n = n.previousSibling );
    }
    return null;
  };
    
  
  //兄貴を探す
  this.previousSibling = function ( ) {
    var n = this.currentNode;
    var r;
    
    while( n = n.previousSibling ) {
      r = filter( n );
      if( 1 == r ) return ( this.currentNode = n );
      if( 2 == r ) return null;
//    if( 3 == r );
    }
    return null;
  };


  //舎弟を探す
  this.nextSibling = function ( ) {
    var n = this.currentNode;
    var r;
    
    while( n = n.nextSibling ) {
      r = filter( n );
      if( 1 == r ) return ( this.currentNode = n );
      if( 2 == r ) return null;
//    if( 3 == r );
    }
    return null;
  };


  //相対的な前のノード
  this.previousNode = (function ( get ) {
    return function ( ) {
      var o, r;
      var current = { node: this.currentNode, depth: depth };
      
      while( ( o = get( current ) ) && 0 < o.depth ) {
        r = filter( o.node );
        if( 1 == r ) return ( depth = o.depth, this.currentNode = o.node );
        if( 2 == r ) return null;
//      if( 3 == r );
      }
      return null;
    };
  })(function ( current ) {
       var n, d = current.depth;
       
       if( n = current.node.previousSibling ) {
         while( n.hasChildNodes( ) )
           n = n.lastChild, d++;
         return { node: n, depth: d };
       }

       return ( n = current.node.parentNode ) ? { node: n, depth: d - 1 }: null;
     });
    
    
  //相対的な次のノード
  this.nextNode = (function ( get ) {
    return function ( ) {
      var o, r;
      var current = { node: this.currentNode, depth: depth };
      
      while( ( o = get( current ) ) && o.node && 0 < o.depth ) {
        r = filter( o.node );
        if( 1 == r ) return ( depth = o.depth, this.currentNode = o.node );
        if( 2 == r ) return null;
//      if( 3 == r );
      }
      return null;
    };
  })(function ( current ) {
       var cn = current.node, d = current.depth, n;
      
       if( n = cn.firstChild )
         return { node: n, depth: d + 1 };

       do
         if( n = cn.nextSibling )
            return { node: n, depth: d };
       while ( d--, cn = cn.parentNode );

       return null;
    });
};