NamedNodeMap.setNamedItem()

setNamedItem(attr);

<span one="one" two="two"></span>
<pre test="testValue"></pre>

const span = document.getElementsByTagName("span")[0];
const pre = document.getElementsByTagName("pre")[0];
const attrMap = pre.attributes;

let result = "The `<pre>` element initially contains " + attrMap.length + " attributes.\n\n";

result += "We remove `one` from `<span>` and adds it to `<pre>`.\n";
const one = span.attributes.removeNamedItem("one");
attrMap.setNamedItem(one);
result += "The `<pre>` element now contains " + pre.attributes.length + " attributes.\n\n";

result += "We get `two` from `<span>` and try to adds it to `<pre>`.\n";
const two = span.attributes.getNamedItem("two");
try {
  attrMap.setNamedItem(two);
}
catch (e) {
  result += "An exception has been raised: " + e.name + ".\n";
}

pre.textContent = result;