What is the difference between static and dynamic web scraping in Ruby?

Static and dynamic web scraping refer to two different approaches to extracting data from web pages, and the distinction lies in how the web page content is generated.

Static Web Scraping: Static web scraping involves extracting data from web pages that are rendered on the server-side and sent to the client as HTML. These pages don't require any additional processing, such as running JavaScript, to display the full content. In Ruby, you can use libraries like Nokogiri to parse the HTML and extract the needed information.

Here's a simple example of static web scraping using Nokogiri in Ruby:

require 'nokogiri'
require 'open-uri'

# Fetch and parse the HTML document
doc = Nokogiri::HTML(URI.open('http://example.com'))

# Use CSS selectors to find the desired data
titles = doc.css('h1, h2, h3').map(&:text) # Get all header text on the page

puts titles

Dynamic Web Scraping: Dynamic web scraping is required when dealing with web pages that rely heavily on JavaScript to render content. These pages execute scripts on the client-side to display the full content, which means that simply fetching the HTML as in static scraping won't reveal all the data. In Ruby, you can use tools like Selenium or Watir in combination with a headless browser like headless Chrome or headless Firefox to interact with the JavaScript on the page and wait for the content to load before scraping.

Below is an example of dynamic web scraping using Watir in Ruby:

require 'watir'

# Set up the browser (make sure you have the corresponding driver, e.g., chromedriver)
browser = Watir::Browser.new :chrome, headless: true

# Navigate to the page
browser.goto 'http://example.com/dynamic-content'

# Wait for a specific element to be present (indicating the content has loaded)
browser.wait_until { |b| b.element(css: 'div.dynamic-content').present? }

# Now you can scrape the content
dynamic_content = browser.element(css: 'div.dynamic-content').text

puts dynamic_content

# Remember to close the browser
browser.close

Key Differences:

1. Content Loading: Static scraping works with content that's already present in the HTML, while dynamic scraping deals with content that gets loaded or altered by JavaScript after the initial page load.

2. Complexity: Static scraping is generally simpler and faster since it involves straightforward HTTP requests and HTML parsing. Dynamic scraping is more complex as it must interact with a browser engine to render the JavaScript.

3. Performance: Static scraping consumes less resources and is quicker because it doesn't require a browser engine. Dynamic scraping is more resource-intensive and slower due to the overhead of browser automation.

4. Libraries and Tools: Different tools are used for each type of scraping. For static scraping, libraries like Nokogiri are sufficient. For dynamic scraping, tools like Selenium or Watir with a headless browser are necessary.

5. Robustness: Dynamic scraping is often more robust to changes in how a website loads content, as it simulates a real user's interaction with the browser. However, it can be more prone to breakage if the website changes its JavaScript code or interactions.

When choosing between static and dynamic web scraping in Ruby, consider the nature of the web page you're targeting and select the approach that suits your needs while being mindful of the website's terms of service and scraping ethics.