NamedNodeMap.getNamedItem()

getNamedItem(name);
[name];

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

const pre = document.getElementsByTagName("pre")[0];
const attrMap = pre.attributes;
let result = `The 'test' attribute contains ${
  attrMap.getNamedItem("test").value
}\n`;
if (attrMap["boum"]) {
  result += "And 'boum' has been found.";
} else {
  result += "And 'boum' has not been found.";
}
pre.textContent = result;