问题:为什么点击li，在控制台出现的是4，而不是对应的索引号？
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<nav>
<li>柚子</li>
<li>苹果</li>
<li>香蕉</li>
<li>李子</li>
</nav>
<script>
var lis = document.querySelectorAll('li')
for(var i =0;i<lis.length;i++){
lis[i].onclick = function(){
console.log(i);
}
}
</script>
</body>
</html>
