artTemplate如何进行变量运算
```
<script id="left_sidebar_tpl" type="text/html">
                <ul class="nav_list">
            <% var i = isNaN(parseInt(cur_top))?0:parseInt(cur_top); %>
            <% for (var m = 0, len = list[i].submenu.length; m < len; m++){ %>

                <li>
                <% if (list[i].submenu[m].sub === 'none') { %>
                    <a href="<%= list[i].submenu[m].link %>"><h3><%= list[i].submenu[m].name %></h3></a>

                <% } %>
                <% else { %>
                    <h3><%= list[i].submenu[m].name %><i class="fa fa-angle-down"></i></h3>
                    <ul class="submenu">

                        <% for(var n =0, l = list[i].submenu[m].sub.length; n < l; n++) { %>

                            <li><a href="<%= list[i].submenu[m].sub[n].sublink %>"><%= list[i].submenu[m].sub[n].subname %></a></li>

                        <% } %>

                    </ul>
                <% } %>

                </li>

            <% } %>
                </ul>
</script>
```

这个是data值：

```
var data = {
    desc: '顶级导航区域',
    list: [
        {
            anchor: '#1', icon: 'fa-home', title: '控制台', 
            submenu: [
                {link: '#gy', name: '概要', sub:'none'},
                {
                    link: '#zx', name: '杂项', sub: [
                        {sublink: '#wg', subname: '外观'},
                        {sublink: '#cj', subname: '插件'},
                        {sublink: '#mb', subname: '模版'}
                    ]
                }
            ]
        },
        {
            anchor: '#2', icon: 'fa-edit', title: '内容管理', 
            submenu: [
                {
                    link: '#wz', name: '文章管理', sub: [
                        {sublink: '#lb', subname: '文章列表'},
                        {sublink: '#zxxwz', subname: '撰写新文章'},
                        {sublink: '#tag', subname: '标签'},
                        {sublink: '#cat', subname: '分类'}
                    ]
                },
                {link: '#dy', name: '单页', sub: 'none'},
                {link: '#yl', name: '友链', sub: 'none'},
                {link: '#ht', name: '幻图', sub: 'none'}
            ]
        }
    ],
    cur_top:1  //顶级导航高亮索引
};
```

我现在需要在模版里面对传入的变量进行运算比较操作，而不是直接输出经运算过后的变量，所谓helper是在模版输出变量，我在这方面就没看到资料。请问如何解决？不知道为啥artTemplate要禁用一些常规js方法，难道只能使用`if` `for` `=`吗？
