text: const Koa = require('koa');
  
  let koaInstance = null;
  
  /**
   * 实例化Koa，单例模式
   */
  function getKoaInstance() {
    if (!koaInstance) {
      koaInstance = new Koa();
      return koaInstance;
    }
    return koaInstance;
  }
  
  module.exports = getKoaInstance;
  