第7题：

        function Dom2JSON(str) {
            function helper(str) {
                let reg = /<(.+)>(.*?)<\/\1>/g;
                let result = null;
                let nodes = [];
                while ((result = reg.exec(str)) != null) {
                    let currentNode = createJSON(result[1]);
                    nodes.push(currentNode);
                    let children = helper(result[2]);
                    if (children.length != 0) currentNode.children = children;
                }
                return nodes;
            }
            let result = helper(str);
            result = result.length !== 0 ? result[0] : result;
            return JSON.stringify(result);
        }