test.html

<html>
<head>

<style>
body {
    /* height: 1500px; */
}
/* * {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
} */


#AA {
    position: relative;
    /* top: 50px; */
    /* background-color: green; */
    border-color: green;
    border-style: solid;
    /* border-radius: 2px; */
}

#BB {
    /* position: relative; */
    /* background-color: red; */
  /* top: -20px;
  left: 20px;
  background-color: red;
  width: 500px; */
    
}

#CC {
    position: relative;
    /* top: 50px; */
    background-color: yellow;
}


div {
 	position: relative;		/* 相对定位或绝对定位均可 */
 	/* width:500px; */
 	/* height:300px; */
 	top: 50%;
 	/* left: 50%; */
 	/* margin: -150px 0 0 -250px;     	外边距为自身宽高的一半 */
 	background-color: pink;	 	/* 方便看效果 */
    margin: 0 auto;
  }

</style>
</head>
<body>
<!-- <div id="AA">
    <h1>HELLO AAAAAAA</h1>
    <h2>WORLD AAAAAA</h2>
    <div id="CC">
            <h1>HELLO CCC</h1>
            <h2>WORLD CCCCC</h2>
    </div>
</div> -->
<div id="BB">
    <h1>HELLO BBBBB</h1>
    <h2>WORLD BBBB</h2>
</div>
<script>

console.log(window.fun1);
console.log(window.fun2);
console.log(window.fun3);
fun1('fun1');
fun2('fun2');
fun3('fun3');
// console.log(typeof window.fun1);
// console.log(typeof window.fun2);
// console.log(window);

function fun1(params) {
    this.name = 'fun1';
    console.log(this.name)
}

const fun2 = function (params) {
    this.name = 'fun2';
    console.log(this.name)
}

</script>
</body>

</html>