This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The read-only length property of the NamedNodeMap interface is the number of objects stored in the map.
A number containing the number of objects in the map
<pre class="foo" id="bar" contenteditable></pre>
const pre = document.querySelector("pre");
const attrMap = pre.attributes;
pre.textContent = `The 'test' attribute contains ${attrMap.length} attributes.\n`;
| Specification |
|---|
| DOM> # dom-namednodemap-length> |
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | WebView on iOS | |
length |
1 | 12 | 1 | ≤12.1 | 1 | 18 | 4 | ≤12.1 | 1 | 1.0 | 4.4 | 1 |
© 2005–2025 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/NamedNodeMap/length