extjs 部署时动态切换上下文路径

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<script type="text/javascript">
    // 获取首页上下文路径
    var basePath = window.kk;
    basePath = basePath.substr(0, basePath.lastIndexOf('index.html'));
    // 创建base标签
    var base = document.createElement("base");
    base.setAttribute("href", basePath);
    document.getElementsByTagName('head')[0].appendChild(base);

    var Ext = Ext || {};
    ...