The read-only prefix
property of the Attr
returns the namespace prefix of the attribute, or null
if no prefix is specified.
The prefix is always in lower case, whatever case is used at the attribute creation.
Note: Only XML supports namespaces. HTML does not. That means that the prefix of an attribute of an HTML element will always be null
.
Also, only the xml
(for the xml:lang
attribute), xlink
(for the xlink:href
, xlink:show
, xlink:target
and xlink:title
attributes) and xpath
namespaces are supported, and only on SVG and MathML elements.
A string containing the prefix of the namespace the attribute belongs too. If none, it returns null
.
<svg xml:lang="en-US" class="struct" height="1" width="1">Click me</svg>
<label xml:lang="en-US" class="struct"></label>
<p>
<button>Show value for <svg></button>
<button>Show value for <label></button>
</p>
<p>
Prefix of the attribute <code>xml:lang</code>:
<output id="result">None.</output>
</p>
const elements = document.querySelectorAll(".struct");
const buttons = document.querySelectorAll("button");
const outputEl = document.querySelector("#result");
let i = 0;
for (const button of buttons) {
const element = elements[i];
button.addEventListener("click", () => {
const attribute = element.attributes[0];
outputEl.value = attribute.prefix;
});
i++;
}