重要的关键字

  <div id="key"></div>
  <script>
    const output = document.getElementById("key");
    var num = 10;
    function printNum() {
      output.innerHTML += "内部函数：" + num + "<br>";
    }
    this.printNum();
    output.innerHTML += "外部函数：" + this.num + "<br>";
  </script>