NamedNodeMap.removeNamedItem()

removeNamedItem(attrName);

<pre test="testValue"></pre>

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

let result = "The `test` attribute initially contains `" + attrMap["test"].value + "`.\n";

result += "We remove it.\n\n";
attrMap.removeNamedItem("test");

if (attrMap.getNamedItem("test")) {
  result += "And `test` still exists.";
}
else {
  result += "And `test` is no more to be found.";
}

pre.textContent = result;