Node: lookupNamespaceURI() method

lookupNamespaceURI(prefix)

<div class="hidden">
  <div>Test HTML element</div>
  <svg>
    <text>Test SVG element</text>
  </svg>
  <math>Test MathML element</math>
</div>
<table>
  <thead>
    <tr>
      <th><code>prefix</code></th>
      <th><code>&lt;div&gt;</code></th>
      <th><code>&lt;svg&gt;</code></th>
      <th><code>&lt;math&gt;</code></th>
    </tr>
  </thead>
  <tbody></tbody>
</table>

.hidden {
  display: none;
}

const htmlElt = document.querySelector("div");
const svgElt = document.querySelector("svg");
const mathElt = document.querySelector("math");
const tbody = document.querySelector("tbody");
for (const prefix of ["xmlns", "xml", "html", "svg", "xlink", "", null]) {
  const row = document.createElement("tr");
  tbody.appendChild(row);
  row.appendChild(document.createElement("td")).textContent =
    JSON.stringify(prefix);
  for (const el of [htmlElt, svgElt, mathElt]) {
    console.log(el, prefix, el.lookupNamespaceURI(prefix));
    row.appendChild(document.createElement("td")).textContent = String(
      el.lookupNamespaceURI(prefix),
    );
  }
}