Extracting Data from Web Pages

Extracting data from web pages requires navigating the DOM, executing JavaScript, and handling dynamic content. This recipe shows how to use bdg to extract structured data efficiently.

Scenario

You need to extract product information from an e-commerce site:

Product titles, prices, and ratings
Availability status
Customer reviews
Dynamic content loaded via JavaScript

The data will be used for price monitoring or analysis.

Workflow

Start session and wait for page load

Navigate to the target page and ensure all dynamic content has loaded.

bdg https://example.com/products

# Wait for JavaScript execution to complete
sleep 3

# Check if key content is present
bdg dom query ".product-card"

Expected output:

Found 24 nodes matching: .product-card
[0] <div class="product-card" data-id="123">
[1] <div class="product-card" data-id="124">
...

Extract data using JavaScript evaluation

Use bdg dom eval to execute JavaScript and extract structured data.

# Extract all product data as JSON
bdg dom eval '
Array.from(document.querySelectorAll(".product-card")).map(card => ({
  id: card.dataset.id,
  title: card.querySelector(".product-title")?.textContent?.trim(),
  price: card.querySelector(".product-price")?.textContent?.trim(),
  rating: card.querySelector(".rating")?.getAttribute("aria-label"),
  inStock: card.querySelector(".in-stock") !== null,
  url: card.querySelector("a")?.href
}))
' --json

Expected output:

{
  "result": {
    "type": "object",
    "value": [
      {
        "id": "123",
        "title": "Wireless Headphones",
        "price": "$79.99",
        "rating": "4.5 out of 5 stars",
        "inStock": true,
        "url": "https://example.com/products/123"
      },
      {
        "id": "124",
        "title": "Bluetooth Speaker",
        "price": "$49.99",
        "rating": "4.2 out of 5 stars",
        "inStock": false,
        "url": "https://example.com/products/124"
      }
    ]
  }
}

Use accessibility tree for semantic data

The accessibility tree provides semantic structure without HTML noise.

# Query for product elements by role
bdg dom a11y query role=article

# Get semantic representation (70-99% token reduction)
bdg dom get ".product-card" --json

Expected output:

{
  "node": {
    "role": "article",
    "name": "Wireless Headphones",
    "description": "$79.99, 4.5 stars",
    "focusable": true
  }
}

This is more token-efficient than parsing full HTML.

Handle pagination to extract all pages

Navigate through paginated results to collect complete dataset.

# Extract first page
bdg dom eval 'Array.from(document.querySelectorAll(".product-card")).map(c => ({title: c.querySelector(".product-title").textContent}))' --json > page1.json

# Click "Next" button
bdg dom click ".pagination-next"
sleep 2

# Extract second page
bdg dom eval 'Array.from(document.querySelectorAll(".product-card")).map(c => ({title: c.querySelector(".product-title").textContent}))' --json > page2.json

# Merge results
jq -s 'add' page1.json page2.json > all-products.json

Scroll to load lazy-loaded content

Some sites load content only when scrolled into view.

# Scroll to bottom to trigger lazy loading
bdg dom scroll --bottom

# Wait for content to load
sleep 2

# Check if more products appeared
bdg dom query ".product-card" --json | jq '.data.nodes | length'

# Extract all (including lazy-loaded)
bdg dom eval 'document.querySelectorAll(".product-card").length'

Extract data from specific product page

Navigate to a product detail page and extract comprehensive data.

# Navigate to product page via JavaScript
bdg dom eval 'window.location.href = "https://example.com/products/123"'

# Or click a product link
bdg dom click ".product-card:first-child a"

# Wait for navigation
sleep 3

# Extract detailed product data
bdg dom eval '
({
  title: document.querySelector(".product-title")?.textContent,
  price: document.querySelector(".price")?.textContent,
  description: document.querySelector(".description")?.textContent,
  images: Array.from(document.querySelectorAll(".product-image img")).map(img => img.src),
  specifications: Array.from(document.querySelectorAll(".specs tr")).map(row => ({
    name: row.querySelector("th")?.textContent,
    value: row.querySelector("td")?.textContent
  })),
  reviews: Array.from(document.querySelectorAll(".review")).map(review => ({
    author: review.querySelector(".author")?.textContent,
    rating: review.querySelector(".rating")?.getAttribute("aria-label"),
    text: review.querySelector(".review-text")?.textContent
  }))
})
' --json > product-123.json

Handle dynamic content (AJAX-loaded)

Wait for AJAX content to load before extraction.

# Trigger action that loads content
bdg dom click "#load-reviews"

# Wait for network activity to complete
sleep 2

# Verify content loaded by checking network
bdg network list --filter "domain:api.example.com" --last 1

# Extract newly loaded content
bdg dom query ".review" --json | jq '.data.nodes | length'

Extract tabular data

For data in HTML tables, extract as structured JSON.

# Extract table data
bdg dom eval '
Array.from(document.querySelectorAll("table tbody tr")).map(row => {
  const cells = Array.from(row.querySelectorAll("td"));
  return {
    product: cells[0]?.textContent?.trim(),
    price: cells[1]?.textContent?.trim(),
    stock: cells[2]?.textContent?.trim()
  };
})
' --json | jq '.result.value' > products-table.json

Expected output (products-table.json):

[
  {"product": "Laptop", "price": "$999", "stock": "In Stock"},
  {"product": "Mouse", "price": "$29", "stock": "Out of Stock"},
  {"product": "Keyboard", "price": "$79", "stock": "In Stock"}
]

Export complete session data

Stop the session to capture final DOM snapshot.

bdg stop

# Extract DOM from session file
cat ~/.bdg/session.json | jq '.data.dom.html' > full-page.html

# Extract accessibility tree
cat ~/.bdg/session.json | jq '.data.dom.a11yTree' > a11y-tree.json

Extraction Patterns

Extract all links

bdg dom eval 'Array.from(document.querySelectorAll("a")).map(a => ({text: a.textContent.trim(), href: a.href}))' --json | jq '.result.value'

Extract images with alt text

bdg dom eval 'Array.from(document.querySelectorAll("img")).map(img => ({src: img.src, alt: img.alt}))' --json | jq '.result.value'

Extract form field values

bdg dom form --json | jq '.data.forms[0].fields[] | {label, value}'

Extract meta tags

bdg dom eval 'Array.from(document.querySelectorAll("meta")).reduce((acc, meta) => {const name = meta.name || meta.property; if (name) acc[name] = meta.content; return acc}, {})' --json | jq '.result.value'

Extract JSON-LD structured data

bdg dom eval 'Array.from(document.querySelectorAll("script[type=\"application/ld+json\"]")).map(s => JSON.parse(s.textContent))' --json | jq '.result.value'

Common Challenges

Content loaded via infinite scroll

Solution: Scroll incrementally and check for new content.

# Scroll down in chunks
for i in {1..10}; do
  bdg dom scroll --down 500
  sleep 1
  COUNT=$(bdg dom query ".product-card" --json | jq '.data.nodes | length')
  echo "Items loaded: $COUNT"
done

Dynamic class names (React/CSS modules)

Solution: Use stable attributes like data-testid or semantic roles.

# Instead of brittle class names
# ❌ bdg dom query ".css-1x2y3z4"

# Use data attributes
bdg dom query "[data-testid='product-card']"

# Or accessibility roles
bdg dom a11y query role=article

Content in iframes

Solution: Use CDP to switch to iframe context.

# List all frames
bdg cdp Page.getFrameTree --json

# Execute in specific frame (requires CDP scripting)
# Note: Direct iframe support is limited; consider extracting iframe src and navigating to it
bdg dom eval 'document.querySelector("iframe").src'

JavaScript-rendered content with delay

Solution: Poll for element existence before extraction.

# Wait for element to appear
for i in {1..10}; do
  EXISTS=$(bdg dom query ".dynamic-content" --json | jq '.data.nodes | length')
  if [ $EXISTS -gt 0 ]; then
    echo "Content loaded"
    break
  fi
  sleep 1
done

# Extract content
bdg dom eval 'document.querySelector(".dynamic-content").textContent'

Full Extraction Script Example

Automated product data extraction:

#!/bin/bash
# extract-products.sh

URL="https://example.com/products"
OUTPUT="products-$(date +%Y%m%d-%H%M%S).json"

echo "Starting extraction from $URL"
bdg $URL

# Wait for page load
sleep 3

# Extract product count
TOTAL=$(bdg dom query ".product-card" --json | jq '.data.nodes | length')
echo "Found $TOTAL products"

# Extract all product data
bdg dom eval '
Array.from(document.querySelectorAll(".product-card")).map((card, index) => ({
  index,
  id: card.dataset.id,
  title: card.querySelector(".product-title")?.textContent?.trim(),
  price: card.querySelector(".product-price")?.textContent?.trim(),
  priceNumeric: parseFloat(card.querySelector(".product-price")?.textContent?.replace(/[^0-9.]/g, "")),
  currency: card.querySelector(".product-price")?.textContent?.match(/[$€£]/)?.[0],
  rating: parseFloat(card.querySelector(".rating")?.getAttribute("aria-label")?.match(/[0-9.]+/)?.[0]),
  reviewCount: parseInt(card.querySelector(".review-count")?.textContent?.match(/[0-9]+/)?.[0]),
  inStock: card.querySelector(".in-stock") !== null,
  imageUrl: card.querySelector("img")?.src,
  url: card.querySelector("a")?.href
}))
' --json | jq '.result.value' > $OUTPUT

echo "Extracted $(jq 'length' $OUTPUT) products to $OUTPUT"

# Summary statistics
echo "\nSummary:"
echo "  In stock: $(jq '[.[] | select(.inStock)] | length' $OUTPUT)"
echo "  Out of stock: $(jq '[.[] | select(.inStock | not)] | length' $OUTPUT)"
echo "  Avg price: $$(jq '[.[] | .priceNumeric] | add / length' $OUTPUT)"
echo "  Avg rating: $(jq '[.[] | .rating] | add / length' $OUTPUT)"

bdg stop
echo "Extraction complete"

Best Practices

Use semantic queries for reliability

Accessibility attributes are more stable than CSS classes:

# Prefer
bdg dom a11y query role=button,name="Add to Cart"

# Over
bdg dom query ".btn-primary.add-cart.css-xyz"

Extract incrementally

Don’t load everything into memory at once:

# Extract and save page by page
for page in {1..10}; do
  bdg dom eval "/* extraction script */" --json > "page-$page.json"
  bdg dom click ".next-page"
  sleep 2
done

Validate extracted data

Check for missing or malformed data:

jq '[.[] | select(.title == null or .price == null)] | length' products.json

Next Steps

JavaScript Evaluation

Learn bdg dom eval command in detail

Accessibility Tree

Use semantic queries for data extraction

DOM Commands

Master DOM querying and inspection

CDP Access

Access raw CDP methods for advanced use cases

Common Tasks

Scenario

Workflow

Extraction Patterns

Extract all links

Extract images with alt text

Extract form field values

Extract meta tags

Extract JSON-LD structured data

Common Challenges

Full Extraction Script Example

Best Practices

Use semantic queries for reliability

Extract incrementally

Validate extracted data

Next Steps

JavaScript Evaluation

Accessibility Tree

DOM Commands

CDP Access

Build docs developers (and LLMs) love

Common Tasks

Documentation Index

​Scenario

​Workflow

​Extraction Patterns

​Extract all links

​Extract images with alt text

​Extract form field values

​Extract meta tags

​Extract JSON-LD structured data

​Common Challenges

​Full Extraction Script Example

​Best Practices

​Use semantic queries for reliability

​Extract incrementally

​Validate extracted data

​Next Steps

JavaScript Evaluation

Accessibility Tree

DOM Commands

CDP Access

Build docs developers (and LLMs) love

Scenario

Workflow

Extraction Patterns

Extract all links

Extract images with alt text

Extract form field values

Extract meta tags

Extract JSON-LD structured data

Common Challenges

Full Extraction Script Example

Best Practices

Use semantic queries for reliability

Extract incrementally

Validate extracted data

Next Steps