splice在js中的问题

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>数组</title>
<script type="text/javascript">
var arr=['A','B','C','D','E','F'];
//arr.splice(2,2);
//document.write(arr);为什么给这句话用变量存起来，值就变了，这句话输出ABEF
var arr2=arr.splice(2,2);
document.write(arr2);//输出CD
//ps新手，求解答，先谢过
</script>
</head>