node.js mssql：错误：全局连接已存在。首先调用sql.close（）

Question

我有以下基于this文档的代码：

(async () => {
  try {
    const pool = await mssql.connect(source.connstring);
    const result = await pool.request().query(source.query);
    console.dir(result);
    pool.close(); // also tried with mssql.close();
  } catch (err) {
    if (pool) pool.close();
    console.log(err);
  }
})();

第一次运行正常，第二次（使用不同的source.connstring）则出现以下错误：

Error: Global connection already exists. Call sql.close() first.
    at Object.connect ([...]my_project\db_crawler\node_modules\mssql\lib\base.js:1636:31)
    at [...]my_project\db_crawler\db_crawler.ts:92:58
    at step ([...]my_project\db_crawler\db_crawler.ts:33:23)
    at Object.next ([...]my_project\db_crawler\db_crawler.ts:14:53)
    at [...]my_project\db_crawler\db_crawler.ts:8:71
    at new Promise (<anonymous>)
    at __awaiter ([...]my_project\db_crawler\db_crawler.ts:4:12)
    at [...]my_project\db_crawler\db_crawler.ts:86:27
    at readFromSource ([...]my_project\db_crawler\db_crawler.ts:110:11)
    at [...]my_project\db_crawler\db_crawler.ts:62:57

我发现了两个类似的问题，但我似乎无法解决。