Question

var a = (function(){
                    var Tree = function(obj){
                        if (obj instanceof Object) {
                            //public variable
                            this.root = obj.root || this;
                            this.name = obj.name || "";
                            this.childs = obj.childs || [];
                            this.left = obj.left || null;
                            this.right = obj.right || null;
                            this.parent = obj.parent || null;
                            this.siblings = obj.siblings || [];
                        }
                        else{
                            throw new TypeError("argument is not Object \n needle : [Object]")
                        }
                    },
                    fn = Tree.prototype;
                    fn.add = function(childName){
                        var childObj = {},
                            childLen = this.childs.length;
                        if (typeof childName === "string") {
                            childObj.root = this.root;                                                      //root
                            childObj.name = childName;                                                      //name
                            childObj.childs = [];                                                           //childs
                            childObj.left = (childLen > 0) ? this.childs[childLen - 1] : null;              //left
                            childObj.right = null;                                                          //right
                            childObj.parent = this;                                                         //parent
                            childObj.siblings = this.childs;                                                //siblings

                            childObj = new Tree(childObj);
                            this.childs.push(childObj);                                                     //parent Childs
                            if (childLen > 0) {
                                this.childs[childLen].right = childObj;                                         //right(left's right)
                            }
                        }
                        return this;
                    };
                    /**
                     * @param  {Object} arg
                     * @description {
                     *      name : node name,
                     *      area : findZone,
                     *      find : onTree Find event
                     * }
                     */
                    fn.call = function(arg){
                        var nextNode = {},area = {};
                        if (arg instanceof Object) {
                            if (arg.name instanceof String) {
                                arg.area = (!arg.area instanceof Tree) ? this : arg.area;
                                area = arg.area;
                                nextNode = area.next();
                                arg.always.apply(area, [area]);
                                if (arg.name != area.name) {
                                    this.call(Object.assign(arg,{area : nextNode}));
                                }
                                else if(arg.name === area.name){
                                    if(typeof arg.find === "function"){
                                        arg.find.apply(area, []);
                                    }
                                    else{
                                        return area;
                                    }
                                }
                            }
                            else{
                                throw new TypeError("name only String");
                            }
                        }
                        else{
                            throw new TypeError("argument only Object");
                        }
                    };
                    fn.next = function() {
                        return (this.right != null) ? this.right : this.childs[0];
                    };
                    fn.pre = function() {
                        return (this.left != null) ? this.left : this.parent;
                    };
                    return new Tree({});
                })()