This code reads an HTML file, parses it, serializes it to XHTML, and then parses the XHTML string as an XML document using various Node.js modules. It then uses an XPath expression to select specific nodes from the XML document and logs the selected nodes to the console.

Cell 7

const fs = require('mz/fs');
const xpath = require('xpath');
const parse5 = require('parse5');
const xmlser = require('xmlserializer');
const dom = require('xmldom').DOMParser;

(async () => {
    const html = await fs.readFile('./test.htm');
    const document = parse5.parse(html.toString());
    const xhtml = xmlser.serializeToString(document);
    const doc = new dom().parseFromString(xhtml);
    const select = xpath.useNamespaces({"x": "http://www.w3.org/1999/xhtml"});
    const nodes = select("//x:a/@href", doc);
    console.log(nodes);
})();

// Import required modules
const fs = require('fs/promises'); // Use promises version for async functionality
const { parse } = require('parse5'); // Import specific function to avoid namespace pollution
const { serializeToString } = require('xmlserializer'); // Import specific function to avoid namespace pollution
const { DOMParser } = require('xmldom'); // Use import for ES6 compatibility
const { select } = require('xpath'); // Import specific function to avoid namespace pollution
const { useNamespaces } = require('xpath'); // Import specific function to avoid namespace pollution

// Define constants for namespace and file path
const XHTML_NAMESPACE = 'http://www.w3.org/1999/xhtml';
const FILE_PATH = './test.htm';

// Define async function to extract href attributes
async function extractHref() {
  try {
    // Read file asynchronously
    const html = await fs.readFile(FILE_PATH);

    // Parse HTML using parse5
    const document = parse(html.toString());

    // Serialize HTML to XML string
    const xhtml = serializeToString(document);

    // Parse XML string to DOM document
    const doc = new DOMParser().parseFromString(xhtml);

    // Use XPath expression to select href attributes
    const selectNamespace = useNamespaces({ x: XHTML_NAMESPACE });
    const nodes = select("//x:a/@href", doc, selectNamespace);

    console.log(nodes);
  } catch (error) {
    // Log error and continue execution
    console.error(error);
  }
}

// Call async function to extract href attributes
extractHref();

Code Breakdown

Importing Modules

const fs = require('mz/fs');
const xpath = require('xpath');
const parse5 = require('parse5');
const xmlser = require('xmlserializer');
const dom = require('xmldom').DOMParser;

This section imports various Node.js modules:

• fs (mz/fs): A file system module for reading files.
• xpath: A module for evaluating XPath expressions.
• parse5: A parser for parsing HTML and XML documents.
• xmlser (xmlserializer): A module for serializing XML documents to strings.
• dom (xmldom): A module for parsing and manipulating XML documents.

Main Code Block

(async () => {
    //... code...
})();

This is an immediately invoked async function, which executes its contents as soon as it's defined.

Reading the HTML File

const html = await fs.readFile('./test.htm');

This line reads the contents of the file test.htm in the current directory and assigns it to the html variable.

Parsing the HTML Document

const document = parse5.parse(html.toString());

This line parses the HTML document using parse5.parse() and assigns the resulting document node to the document variable.

Serializing the Document to XHTML

const xhtml = xmlser.serializeToString(document);

This line serializes the parsed HTML document to an XHTML string using xmlser.serializeToString() and assigns it to the xhtml variable.

Parsing the XHTML String as an XML Document

const doc = new dom().parseFromString(xhtml);

This line parses the XHTML string as an XML document using xmldom.DOMParser.parseFromString() and assigns the resulting document node to the doc variable.

Evaluating XPath Expression

const select = xpath.useNamespaces({"x": "http://www.w3.org/1999/xhtml"});
const nodes = select("//x:a/@href", doc);

This code:

1. Uses xpath.useNamespaces() to register a namespace with prefix x and URI http://www.w3.org/1999/xhtml.
2. Evaluates an XPath expression //x:a/@href on the doc document node to select all href attributes of elements with tag name a from the XHTML namespace.
3. Assigns the selected nodes to the nodes variable.

Logging the Selected Nodes

console.log(nodes);

This line logs the selected nodes to the console.