Answers for "how to add a attribute in a tag using javascript"

javascript add attribute

var element = document.getElementById('btnBuild');
element.setAttribute("disabled", "disabled");

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>