Cheerio HTML Parsing

You are an expert in Cheerio, Node.js HTML parsing, DOM manipulation, and building efficient data extraction pipelines for web scraping.

Core Expertise

Cheerio API and jQuery-like syntax
CSS selector optimization
DOM traversal and manipulation
HTML/XML parsing strategies
Integration with HTTP clients (axios, got, node-fetch)
Memory-efficient processing of large documents
Data extraction patterns and best practices

Key Principles

Write clean, modular extraction functions
Use efficient selectors to minimize parsing overhead
Handle malformed HTML gracefully
Implement proper error handling for missing elements
Design reusable scraping utilities
Follow functional programming patterns where appropriate

Basic Setup

npm install cheerio axios

Loading HTML

const cheerio = require('cheerio');
const axios = require('axios');

// Load from string
const $ = cheerio.load('<html><body><h1>Hello</h1></body></html>');

// Load with options
const $ = cheerio.load(html, {
  xmlMode: false,           // Parse as XML
  decodeEntities: true,     // Decode HTML entities
  lowerCaseTags: false,     // Keep tag case
  lowerCaseAttributeNames: false
});

// Fetch and parse
async function fetchAndParse(url) {
  const response = await axios.get(url);
  return cheerio.load(response.data);
}

Selecting Elements

CSS Selectors

// By tag
$('h1')

// By class
$('.article')

// By ID
$('#main-content')

// By attribute
$('[data-id="123"]')
$('a[href^="https://"]')  // Starts with
$('a[href$=".pdf"]')      // Ends with
$('a[href*="example"]')   // Contains

// Combinations
$('div.article > h2')     // Direct child
$('div.article h2')       // Any descendant
$('h2 + p')               // Adjacent sibling
$('h2 ~ p')               // General sibling

// Pseudo-selectors
$('li:first-child')
$('li:last-child')
$('li:nth-child(2)')
$('li:nth-child(odd)')
$('tr:even')
$('input:not([type="hidden"])')
$('p:contains("specific text")')

Multiple Selectors

// Select multiple types
$('h1, h2, h3')

// Chain selections
$('.article').find('.title')

Extracting Data

Text Content

// Get text (includes child text)
const text = $('h1').text();

// Get trimmed text
const text = $('h1').text().trim();

// Get HTML
const html = $('div.content').html();

// Get outer HTML
const outerHtml = $.html($('div.content'));

Attributes

// Get attribute
const href = $('a').attr('href');
const src = $('img').attr('src');

// Get data attributes
const id = $('div').data('id');  // data-id attribute

// Check if attribute exists
const hasClass = $('div').hasClass('active');

Multiple Elements

// Iterate with each
const items = [];
$('.product').each((index, element) => {
  items.push({
    name: $(element).find('.name').text().trim(),
    price: $(element).find('.price').text().trim(),
    url: $(element).find('a').attr('href')
  });
});

// Map to array
const titles = $('h2').map((i, el) => $(el).text()).get();

// Filter elements
const featured = $('.product').filter('.featured');

// First/Last
const first = $('li').first();
const last = $('li').last();

// Get by index
const third = $('li').eq(2);

DOM Traversal

Navigation

// Parent
$('span').parent()
$('span').parents()          // All ancestors
$('span').parents('.container')  // Specific ancestor
$('span').closest('.wrapper')    // Nearest ancestor matching selector

// Children
$('ul').children()           // Direct children
$('ul').children('li.active') // Filtered children
$('div').contents()          // Including text nodes

// Siblings
$('li').siblings()
$('li').next()
$('li').nextAll()
$('li').prev()
$('li').prevAll()

Filtering

// Filter by selector
$('li').filter('.active')

// Filter by function
$('li').filter((i, el) => $(el).data('price') > 100)

// Find within selection
$('.article').find('img')

// Check conditions
$('li').is('.active')  // Returns boolean
$('li').has('span')    // Has descendant matching selector

Data Extraction Patterns

Table Extraction

function extractTable(tableSelector) {
  const $ = this;
  const headers = [];
  const rows = [];

  // Get headers
  $(tableSelector).find('th').each((i, el) => {
    headers.push($(el).text().trim());
  });

  // Get rows
  $(tableSelector).find('tbody tr').each((i, row) => {
    const rowData = {};
    $(row).find('td').each((j, cell) => {
      rowData[headers[j]] = $(cell).text().trim();
    });
    rows.push(rowData);
  });

  return rows;
}

List Extraction

function extractList(selector, itemExtractor) {
  return $(selector).map((i, el) => itemExtractor($(el))).get();
}

// Usage
const products = extractList('.product', ($el) => ({
  name: $el.find('.name').text().trim(),
  price: parseFloat($el.find('.price').text().replace('$', '')),
  image: $el.find('img').attr('src'),
  link: $el.find('a').attr('href')
}));

Pagination Links

function extractPaginationLinks() {
  return $('.pagination a')
    .map((i, el) => $(el).attr('href'))
    .get()
    .filter(href => href && !href.includes('#'));
}

Handling Missing Data

// Safe extraction with defaults
function safeText(selector, defaultValue = '') {
  const el = $(selector);
  return el.length ? el.text().trim() : defaultValue;
}

function safeAttr(selector, attr, defaultValue = null) {
  const el = $(selector);
  return el.length ? el.attr(attr) : defaultValue;
}

// Optional chaining pattern
const price = $('.price').first().text()?.trim() || 'N/A';

URL Resolution

const { URL } = require('url');

function resolveUrl(baseUrl, relativeUrl) {
  if (!relativeUrl) return null;
  try {
    return new URL(relativeUrl, baseUrl).href;
  } catch {
    return relativeUrl;
  }
}

// Usage
const baseUrl = 'https://example.com/products/';
$('a').each((i, el) => {
  const href = $(el).attr('href');
  const absoluteUrl = resolveUrl(baseUrl, href);
  console.log(absoluteUrl);
});

Performance Optimization

// Cache selections
const $products = $('.product');
$products.each((i, el) => {
  const $product = $(el);  // Wrap once
  // Use $product multiple times
});

// Limit parsing scope
const $article = $('.article');
const title = $article.find('.title').text();  // Searches only within article

// Use specific selectors
// Good
$('div.product > h2.title')
// Less efficient
$('div').find('.product').find('h2').filter('.title')

Complete Scraping Example

const cheerio = require('cheerio');
const axios = require('axios');

async function scrapeProducts(url) {
  const response = await axios.get(url, {
    headers: {
      'User-Agent': 'Mozilla/5.0 (compatible; MyScraper/1.0)'
    }
  });

  const $ = cheerio.load(response.data);
  const products = [];

  $('.product-card').each((index, element) => {
    const $el = $(element);

    products.push({
      name: $el.find('.product-title').text().trim(),
      price: parseFloat(
        $el.find('.price').text().replace(/[^0-9.]/g, '')
      ),
      rating: parseFloat($el.find('.rating').attr('data-rating')) || null,
      image: $el.find('img').attr('src'),
      url: new URL($el.find('a').attr('href'), url).href,
      inStock: !$el.find('.out-of-stock').length
    });
  });

  return products;
}

// With error handling
async function safeScrape(url) {
  try {
    return await scrapeProducts(url);
  } catch (error) {
    console.error(`Failed to scrape ${url}:`, error.message);
    return [];
  }
}

Key Dependencies

cheerio
axios (HTTP client)
got (alternative HTTP client)
node-fetch (fetch API for Node.js)
p-limit (concurrency control)

Best Practices

Always handle missing elements gracefully
Use specific selectors for better performance
Cache jQuery-wrapped elements when reusing
Normalize extracted text (trim whitespace)
Resolve relative URLs to absolute
Validate extracted data types
Implement rate limiting when scraping multiple pages
Use appropriate User-Agent headers
Handle character encoding issues
Log extraction failures for debugging

cheerio-parsing

Cheerio HTML Parsing

Core Expertise

Key Principles

Basic Setup

Loading HTML

Selecting Elements

CSS Selectors

Multiple Selectors

Extracting Data

Text Content

Attributes

Multiple Elements

DOM Traversal

Navigation

Filtering

Data Extraction Patterns

Table Extraction

List Extraction

Pagination Links

Handling Missing Data

URL Resolution

Performance Optimization

Complete Scraping Example

Key Dependencies

Best Practices