What's the difference between JavaScript DOM selectors and Puppeteer's $x evaluation?

Other Questions Puppeteer
1

I’ve been using Puppeteer for web scraping and I’m a bit confused about selectors. I know how to use XPath with Puppeteer’s $x method, like this:

const [element] = await page.$x('//*[@id="details"]/div/table/tbody/tr[3]/td');

But now I need to use querySelector instead. I tried converting the XPath to a CSS selector:

const element = document.querySelector('#details div > table > tbody > tr:nth-child(3) > td');

It’s not working though. I’m trying to grab the publication field from a WorldCat page. Can someone explain the right way to convert XPath to a CSS selector for use with querySelector? What am I missing here?

I’m new to web scraping and still learning about these methods. Any help would be great!

2

The main difference between DOM selectors and Puppeteer’s $x is the context they operate in. DOM selectors like querySelector work directly in the browser’s JavaScript environment, while Puppeteer’s $x runs in Node.js and interacts with the page remotely.

For your specific case, the XPath to CSS conversion looks correct, but remember that Puppeteer operates differently. Instead of document.querySelector, you’d use page.$ or page.evaluate. Try this:

const element = await page.$('#details div > table > tbody > tr:nth-child(3) > td');

If that doesn’t work, the page structure might be different than expected. You could use page.evaluate to run querySelector directly in the page context and debug:

const element = await page.evaluate(() => {
    const el = document.querySelector('#details div > table > tbody > tr:nth-child(3) > td');
    return el ? el.textContent : null;
});

This approach allows you to see what’s actually being selected on the page.

3

As someone who’s been deep in the trenches of web scraping for years, I can tell you that the transition from XPath to CSS selectors can be tricky. Here’s what I’ve learned:

First off, your CSS selector looks solid, but WorldCat pages can be finicky. They often have dynamic content or iframes that complicate things. Here’s a trick I use:

Instead of relying on the exact structure, try a more flexible approach. Something like:

const element = await page.$eval('td[data-tag=\"260\"]', el => el.textContent);

This targets the publication info directly by its data attribute. It’s more robust against layout changes.

Also, don’t forget to wait for the content to load. I’ve been burned by that more times than I care to admit. Try adding:

await page.waitForSelector('td[data-tag=\"260\"]');

before your selector. This ensures the element is actually there before you try to grab it.

Remember, web scraping is often a game of trial and error. Keep at it!

4

hey there! i’ve done some worldcat scraping before. the tricky part is that their pages load dynamically. try using page.waitForSelector() before grabbing the element. also, their structure can change, so a more flexible selector might work better. something like:

const element = await page.$(‘td[itemprop=“datePublished”]’);

this targets the publication date directly. hope that helps!