Querying and Validating

After the XML is parsed into DOM,

Query Nodes

XmlNode has get and find methods which both use xpath to find the node. Their different is, get returns the first node it found while find returns all of thme.

import { XmlDocument } from 'libxml2-wasm';

const doc = XmlDocument.fromString('<note><to>Amy</to><to>Bob</to></note>');
console.log(doc.root.get('to').content); // Amy
console.log(doc.root.find('to').map((node) => node.content).join()); // Amy,Bob
doc.dispose();
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Although get and find can be used to get attributes of an element, attr() and attrs could be more efficient, because instead of analyzing the xpath string, they search attribute array of the current element directly:

import { XmlDocument } from 'libxml2-wasm';

const doc = XmlDocument.fromString('<line from="left" to="right"/>');
console.log(doc.root.get('@from').content); // left
console.log(doc.root.attr('from').content); // left
console.log(doc.root.find('@*').map((node) => node.content).join()); // left,right
console.log(doc.root.attrs.map((node) => node.content).join()); // left,right
doc.dispose();
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When an XPath is used many times, you could create an XmlXPath object to avoid redundantly parsing XPath string.

import { XmlDocument, XmlXPath } from 'libxml2-wasm';

const xpath = XmlXPath.create('/book/title');
const doc1 = XmlDocument.fromString('<book><title>Harry Potter</title></book>');
const doc2 = XmlDocument.fromString('<book><title>Learning XML</title></book>');
console.log(doc1.get(xpath).content); // Harry Potter
console.log(doc2.get(xpath).content); // Learning XML
doc1.dispose();
doc2.dispose();
xpath.dispose();
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Note that similar to XmlDocument, XmlXPath owns native memory and needs to be disposed explicitly.

Validating XML

To validate an XML with an XSD file, create the validator from the schema first, then use the validator to validate the XML document.

import fs from 'node:fs';
import { XmlDocument, XsdValidator } from 'libxml2-wasm';

const schema = XmlDocument.fromBuffer(fs.readFileSync('schema.xsd'));
const validator = XsdValidator.fromDoc(schema);

const doc = XmlDocument.fromBuffer(fs.readFileSync('document.xml'));
try {
    validator.validate(doc);
} catch (err) {
    console.log(err.message);
}

doc.dispose();
validator.dispose();
schema.dispose();
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XSD Include/Import

xsd:include and xsd:import are supported with virtual IO. See the Virtual IO section of document of Parsing and Serializing

RELAX NG

RELAX NG is also supported, with another validator class RelaxNGValidator.