Visitor Pattern in JavaScript

visitor.js

var calc = {
  add: function (node) {
    return visit(node.l) + visit(node.r);
  },
  sub: function (node) {
    return visit(node.l) - visit(node.r);
  },
  val: function (node) {
    return node.val;
  }
};

var dump = {
  add: function (node) {
    return visit(node.l) + ' + ' + visit(node.r);
  },
  sub: function (node) {
    return visit(node.l) + ' - '  +  visit(node.r);
  },
  val: function (node) {
    return String(node.val);
  }
};

var convert = {
  add: function (node) {
    var currentNode = {n:node.tag};
    
    currentNode.content = currentNode.content || [];
    currentNode.content.push(visit(node.l));
    currentNode.content.push(visit(node.r));
    
    return currentNode;
  },
  sub: function (node) {
    var currentNode = {n:node.tag};
    
    currentNode.content = currentNode.content || [];
    currentNode.content.push(visit(node.l));
    currentNode.content.push(visit(node.r));
    
    return currentNode;
  },
  val: function (node) {
    var currentNode = {n:node.tag, v: node.val};
    return currentNode;
  }
};


var root = {
  tag: 'add',
  l: {
    tag: 'val', 
    val: 2
  },
  r: {
    tag: 'sub',
    l: {
      tag: 'val', 
      val: 3
    },
    r: {
      tag: 'val',
      val: 1
    }
  }
};


var visit = (function() {
  var currentVisitor;
  return function(node, visitor) {
    currentVisitor = visitor || currentVisitor;
    return currentVisitor[node.tag](node);
  };
})();

console.log(visit(root, calc));
console.log(visit(root, dump));
console.log(JSON.stringify(visit(root, convert), null, 4));