EasyUI TreeGrid优化与实现

/**
 *@TreeGrid
 *@version v1.0 初稿
 *@version v1.1 为保持与easyui datagrid样式一致，使用部分easyui样式 .datagrid-
 */
TreeGrid = function (_config) {
    _config = _config || {};

    var s = "";
    var rownum = 0;
    var __root;

    var __selectedData = null;
    var __selectedId = null;
    var __selectedIndex = null;

    var folderOpenIcon = (_config.folderOpenIcon || TreeGrid.FOLDER_OPEN_ICON);
    var folderCloseIcon = (_config.folderCloseIcon || TreeGrid.FOLDER_CLOSE_ICON);
    var defaultLeafIcon = (_config.defaultLeafIcon || TreeGrid.DEFAULT_LEAF_ICON);

    //显示表头行
    drowHeader = function () {
        s += "<tr class='datagrid-header-row' height='" + (_config.headerHeight || "25") + "'>";//class='header' 
        var cols = _config.columns;
        for (i = 0; i < cols.length; i++) {
            var col = cols[i];
            s += "<td align='" + (col.headerAlign || _config.headerAlign || "center") + "' class='datagrid-header' nowrap=true style='"+ (col.hidden ? "display:none;" : "") +"border-style:solid;' width='" + (col.width || "") + "'>" + (col.headerText || "") + "</td>";
        }
        s += "</tr>";
    }

    //递归显示数据行
    drowData = function () {
        var rows = _config.data;
        var cols = _config.columns;
        drowRowData(rows, cols, 1, "");
    }

    //局部变量i、j必须要用 var 来声明，否则，后续的数据无法正常显示
    drowRowData = function (_rows, _cols, _level, _pid) {
        var folderColumnIndex = (_config.folderColumnIndex || 0);

        for (var i = 0; i < _rows.length; i++) {
            var id = _pid + "_" + i; //行id
            var row = _rows[i];

            s += "<tr id='TR" + id + "' data-pid='" + ((_pid == "") ? "0" : ("TR" + _pid)) + "' data-open='N' style='"+(_level > 1 ? "display:none;" : "")+"' data-row='" + TreeGrid.json2str(row) + "' data-rowIndex='" + rownum++ + "' class='datagrid-row"+(i%2 == 1 ? " datagrid-row-alt" : "")+"'>";
            for (var j = 0; j < _cols.length; j++) {
                var col = _cols[j];
                s += "<td align='" + (col.dataAlign || _config.dataAlign || "left") + "' nowrap=true style='";

                //层次缩进
                if (j == folderColumnIndex) {
                    s += "text-indent:" + (parseInt((_config.indentation || "20")) * (_level - 1) + 10) + "px;";
                }
                if(col.hidden){
                 s += "display:none;";
                }
                
                s += "'>";