// 建立语法树
  public void buildSymbolTree() {
    offset = 0;
    braceNesting = 0; // 花括号嵌套
    scopes.clear(); // 清空栈
    indexedScopes.clear(); // 清空哈希表
    indexedScopes.put(new Integer(0), globalScope); // gloabalScope为ScriptOrFnScope对象,构造函数参数为-1,null
    mode = BUILDING_SYMBOL_TREE; // (BUILDING_SYMBOL_TREE值为1)
    parseScope(globalScope);

    globalScope.warning();
  }