text: 
  // because document.write is not allowed in module
  let app = document.getElementById('root');
  
  
  function print(...words) {
      if(words) {
          words.forEach((w)=>app.append(w));
      }
  }
  
  function println(...words) {
      print(words);
      app.insertAdjacentHTML("beforeend", '<br/>');
  }
  
  var a = 2; {
      let a = 3;
      print(a);
  }
  println(a);
  
  const A = "Hello";
  println(A);
  
  class Animal {
      constructor() {
          this.type="One-Animal";
      }
      says(word) {
          println(this.type + " says in cosmos language: " + word);
      }
  }
  let animal = new Animal();
  animal.says("你好！");
  
  class Dog extends Animal {
      constructor(){
          super();
          this.type="A-Dog";
      }
      says(word='汪汪') {
          println(this.type + ' says: ' + word);
      }
  }
  let dog = new Dog();
  dog.says();
  dog.says("欢迎")
  
  
  var f = (i) => i*i;
  println(f(10));
  
  var animalType = `animal's type: ${animal.type}`;
  var dogType =    `dog's type:    ${dog.type}`;
  println(animalType);
  println(dogType);
  
  
  var tic = {type: 'Tic', times: 2}
  let {type, times} = tic;
  println(type, times, JSON.stringify(tic));
  
  import pl from './js/utils'
  pl(app);
  println();
  
  import foo from './js/utils2'
  foo(app);
  println();
  
  import './libs/jquery-3.5.1'
  print('load traditional module jquery -> ')
  println(jQuery.fn.jquery)
  