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;