SOURCE

function insertAfter(newNode, target) {
	let parent = target.parentNode;
	if (parent.lastChild == target) {
		parent.appendChild(newNode);
	} else {
		parent.insertBefore(newNode, target.nextSibling);
	}
}
let content = document.createElement("div");
content.innerHTML = "hello";
insertAfter(content, document.getElementById("link"));

<div>
	<p>haizei</p>
	<p>haizei</p>
	<a href="#" id = "link">链接</a>
	<p>haizei</p>
</div>
<script type="text/javascript" src="insertAfter.js"></script>