How do I debug scripts in Puppeteer?

Debugging scripts in Puppeteer, a Node.js library that provides a high-level API to control Chrome or Chromium over the DevTools Protocol, can be done in several ways. Here's a guide on how to do it:

1. Logging Console Output:

Puppeteer provides an event-driven API that can be used to capture console outputs from the page. This can be very useful for debugging. Here's how you can do this in JavaScript:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  page.on('console', msg => console.log('PAGE LOG:', msg.text()));

  await page.goto('https://example.com');
  // other actions...

  await browser.close();
})();

In this script, we are using Puppeteer's page.on method to listen for the 'console' event, and then we log the console messages from the web page to the Node.js console.

2. Debugging with Chrome DevTools:

You can also debug your Puppeteer code using Chrome DevTools. Just launch Puppeteer with {devtools: true} option and then put debugger; statement in your script where you want the execution to pause:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({devtools: true});
  const page = await browser.newPage();

  await page.goto('https://example.com');
  // other actions...

  debugger;

  await browser.close();
})();

When running this script, it will open a new Chrome window with DevTools opened. The execution will stop at the debugger; statement, allowing you to inspect the page elements, network, and other details in the DevTools.

3. Debugging Node.js Process:

To debug the Node.js process itself, you can use the built-in debugger in Node.js. To do this, you would start your script with node --inspect or node --inspect-brk followed by the script name.

node --inspect-brk myScript.js

This will start the script in debugging mode. You can then open chrome://inspect in a Chromium-based browser and click the "inspect" link under your Node.js process in the "Remote Target" section.

In the opened DevTools, you can add breakpoints, step through your code, inspect variables, and see the call stack. For more details on how to use the Node.js debugger, you can check the official Node.js debugging guide.

Remember, debugging is a powerful tool in understanding and fixing problems in your code, always make sure to use these techniques when you encounter issues in your Puppeteer scripts.