add attribute to element
//This is for creating an attribute with setAttributeNode
<script>
var f = document.querySelector("#menu-item-16 > a");// Get the <a> element
var c = document.createAttribute("target");// Create a "target" attribute
c.value = "_blank"; // Set the value of the target attribute
f.setAttributeNode(c); // Add the target attribute to <a>
</script>
//With setAttribute
<script>
let e = document.querySelector("#menu-item-16 > a");
e.setAttribute("target", "_blank");
</script>