NamedNodeMap.length is a read-only number: how many objects (attributes) are stored in the map. Per MDN, on elements you almost always read element.attributes.length.
Read the notes below before you rely on this property. Prefer feature detection when support is limited.
Use map.length. Start with this line.
namedNodeMap.length| Call | What it does |
|---|---|
namedNodeMap.length | Primary signature. |
Built into the browser. Read map.length on a NamedNodeMap — no import required.
namedNodeMap.lengthThis member has no parameters beyond those shown in the signature.
| Return Value | Description |
|---|---|
| * | The current value of map.length. |
lengthCount attributes on an element (MDN-style).
const pre = document.querySelector("pre");
const attrMap = pre.attributes;
console.log(attrMap.length);
// e.g. 3 for class, id, contenteditableattributes map.length. One number — how many Attrs are stored.map.length = 0.item() or getNamedItem().item()Use length as the loop bound and visit every attribute.
const box = document.querySelector("#demo");
const map = box.attributes;
const names = [];
for (let i = 0; i < map.length; i++) {
names.push(map.item(i).name);
}
console.log(map.length, names.join(", "));i runs from 0 to length - 1.map.item(i) returns one attribute.attr.name (or use value).length changes when you add or remove attributes.
const box = document.querySelector("#demo");
const map = box.attributes;
const before = map.length;
box.setAttribute("title", "Demo box");
const afterAdd = map.length;
box.removeAttribute("class");
const afterRemove = map.length;
console.log(before, afterAdd, afterRemove);setAttribute increases length by 1.removeAttribute decreases it by 1.An element with no attributes has length 0.
const empty = document.querySelector("#empty");
const withAttrs = document.querySelector("#demo");
console.log(empty.attributes.length); // 0
console.log(withAttrs.attributes.length); // e.g. 2<div id="empty"> still has an attributes map.length > 0.null — always a number.hasAttributes()length > 0 matches hasAttributes() for “any attrs?”.
const empty = document.querySelector("#empty");
const demo = document.querySelector("#demo");
console.log(
empty.attributes.length > 0,
empty.hasAttributes(),
demo.attributes.length > 0,
demo.hasAttributes()
);false.true.hasAttributes() for a yes/no; use length when you need the count.NamedNodeMap.length is marked Baseline Widely available on MDN (since July 2015). It is a browser DOM API — not a Node.js built-in.
Supported across modern Chrome, Firefox, Safari, and Edge for counting attributes on an element.
Bottom line: Safe for production. Read attributes.length for the count; use setAttribute/removeAttribute to change it.
Create DOM text nodes with the Text constructor.
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