<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<div class="container">
<div class="item">1</div>
<div class="item">2</div>
<div class="item">3</div>
<div class="item">4</div>
<div class="item">5</div>
<div class="item">6</div>
<div class="item">7</div>
<div class="item">8</div>
</div>
<script>
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el.insertAdjacentHTML('beforebegin', '<div class="item-box"></div>');
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var next = el.nextElementSibling;
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</body>
</html>