Puppeteer is a powerful tool for automating web testing and scraping. However, it is still subject to problems and bugs like any other software.
It's crucial to have a well-thought-out plan for solving issues in place for times like these.
In this post, we'll explore some of the best practices for Puppeteer debugging and troubleshooting with Puppeteer.
16 Puppeteer Debugging and Troubleshooting Tricks & Tips
Are you trying to simplify your Puppeteer testing? Here are the best practices for troubleshooting common issues in Puppeteer:
1. Use console.log() for debugging
The console.log() function is one of Puppeteer's most helpful debugging tools. This function allows you to log information to the console as your code runs, which can be used to track down and fix bugs.
For instance, you can use console.log() to run a Puppeteer test by double-checking that you've identified the right element on a page by inspecting its properties. You can also use console.log() to check the values of variables as your code runs.
2. Enable verbose logging
There is an option in Puppeteer to enable verbose logging, which can give you a lot of information about what's going on while your code is running. Enabling this option can be especially helpful when encountering issues with your code.
You can pass a configuration object to the puppeteer.launch() function with the following options to enable verbose logging:
{
headless: true,
devtools: false,
slowMo: 0,
timeout: 30000,
args: ['--enable-logging,' '--v=1']
}
3. Use try-catch blocks
Another best practice for Puppeteer troubleshooting is to use try-catch blocks in your code. This can help you catch any possible errors and handle them more gracefully.
For example, if you're trying to navigate to a webpage and encounter an error, you can use a try-catch block to handle the error and prevent your code from crashing:
try {
await page.goto('https://www.example.com');
} catch (error) {
console.log('An error occurred:', error);
}
4. Verify the environment
Ensure that your environment is properly configured before beginning Puppeteer troubleshooting. Ensure you have all the necessary dependencies for your code, such as the latest versions of Node.js and Puppeteer.
Run this command in the terminal to determine the Puppeteer version installed on your machine:
npm list puppeteer
5. Use page.waitFor*() instead of setTimeout()
It is common practice to incorporate a delay into Puppeteer scripts to allow the page to load before moving on to the next command. While the setTimeout() function can accomplish this, it is recommended that you instead use the page.waitFor*() function.
With page.waitFor*() functions like waitForFileChooser, waitForSelector, etc., you can pause the execution of a script until a given condition has been fulfilled. You can, for instance, wait for a certain page element to show up before interacting with it:
await page.waitForSelector('#my-element');
await page.click('#my-element');
Using page.waitFor*() can help make your code more robust and reliable, as it ensures that your commands are executed only when the page is ready. Try running a Puppeteer test and see the difference!
6. Handle network errors
Sometimes, your Puppeteer script might encounter network errors when accessing a webpage. This can happen if the page is down or your internet connection is weak.
The page.on('requestfailed') event can be used to monitor for requests that fail over a network and react accordingly. For example, you can log the error or retry the request:
page.on('requestfailed', request => {
console.log(request.failure().errorText);
});
7. Check the page's state
If you're using Puppeteer to manipulate a page, it's smart to periodically inspect its state and ensure your changes took effect as intended. You can use the page.waitForNavigation() function to wait for the page to finish loading before proceeding, and the page.waitForSelector() function to wait for an element to appear on the page.
You can also check the page's URL to make sure that you're on the correct page:
const url = await page.url();
if (url !== 'https://www.example.com') {
console.log('Incorrect page navigated');
}
Validating the current page state before continuing with Puppeteer code execution can help catch and fix assumptions-based bugs.
8. Use the --no-sandbox flag
When you run Puppeteer, it will launch Chromium in a sandbox by default. This adds a layer of protection but may also prevent your code from running properly.
This sandbox may not function as intended in certain environments, such as when Puppeteer is being run inside a container or a virtual machine.
For example, If you're running Puppeteer on a Linux machine, you might encounter an error when trying to launch a browser instance. This is because the default sandbox configuration in Linux is not compatible with Puppeteer.
You can launch Chromium without the sandbox by specifying the --no-sandbox flag when launching:
const browser = await puppeteer.launch({ args: ['--no-sandbox'] });
This can help resolve issues related to containerization or virtualization.
9. Emulate different devices
Puppeteer lets you simulate various devices and screen sizes, allowing you to test your site's functionality across multiple platforms. This can be useful for finding design and responsiveness issues on your site.
You can use the page.emulate() function and pass in a device configuration to emulate a device:
await page.emulate(puppeteer.devices['iPhone X']);
This will emulate the iPhone X's screen size and other device properties, allowing you to test your website as if you were using an iPhone X.
10. Use descriptive error messages
Descriptive error messages are invaluable when debugging Puppeteer code because they allow you to zero in on the exact nature of the problem. For example, instead of simply logging "Error," you might log a more specific error message that tells you what went wrong:
try {
await page.goto('https://www.example.com');
} catch (error) {
console.log('An error occurred while navigating to the page:', error);
}
To generalize, it's a good idea to include as much information as possible in your error messages. This will help you identify the root cause of the problem more quickly.
try {
// some Puppeteer code
} catch (error) {
console.error(`Error case description: ${error.message}`);
}
Descriptive error messages make it easier to determine what went wrong and what needs to be done to fix it.
11. Use page.on('error')
The page.on('error') event can be used to catch errors that occur in the page context. This can be useful for debugging issues that occur in the browser, such as JavaScript errors.
For example, you can use the page.on('error') event to log JavaScript errors that occur on the page:
page.on('error', error => {
console.log('Error in page context:', error);
});
12. Use page.on('console')
Puppeteer provides a page.on('console') event that allows you to listen for messages logged to the page's console. This can help debug Puppeteer tests and identify issues with your website.
For example, use the page.on('console') event to log messages that are printed to the console:
page.on('console', (message) => {
console.log(`Message: ${message.text()}`);
});
Monitoring the console can help you determine where your website is experiencing problems and what steps need to be taken to fix them.
13. Avoid using page.evaluate() for complex operations
The page.evaluate() function is useful for running JavaScript code within the page's context, but it can be slow for more involved computations. This is because page.evaluate() has to serialize the data back and forth between the browser and Node.js.
If you're looking to boost the performance of your Puppeteer code, try running complex operations directly in Node.js rather than through page.evaluate(). This can help speed up your code and improve its reliability.
For example, instead of using page.evaluate() to manipulate a large dataset, you might use a Node.js library like Lodash to operate. This makes Puppeteer testing easier.
14. Use timeouts to handle slow-loading pages
Puppeteer provides a page.setDefaultNavigationTimeout() function that allows you to set a default timeout for page navigation operations. This can be useful for handling slow-loading pages that might otherwise cause your script to hang.
For example, you might set a default navigation timeout of 10 seconds:
page.setDefaultNavigationTimeout(10000);
This will cause Puppeteer to throw an error if a page navigation operation takes longer than 10 seconds.
You can also set a specific timeout for individual navigation operations using the timeout option:
await page.goto('https://www.example.com', { timeout: 10000 });
This will cause Puppeteer to generate an error if the goto() operation takes longer than 10 seconds.
15. Check the status of requests and responses
You can monitor network requests and responses with Puppeteer's page.on('response') event. This can help you find slow-loading resources and diagnose performance issues on your site.
For example, use the page.on('response') event to log the status code of each response:
page.on('response', response => {
console.log('Response status:', response.status());
});
If you keep track of the response status code for each request, you can easily find out which ones are returning errors or taking too long to complete.
16. Use descriptive variable names
Use descriptive names for variables in your Puppeteer code that convey their function. For example, instead of using a variable named x, you might use a variable named username to store the username input field on a login page.
The descriptive names for variables improve readability and help to debug Puppeteer tests.
Conclusion
Although Puppeteer debugging can be difficult, these best practices will make the process much easier. Check your environment, use try-catch blocks, and enable verbose logging and console.log() for debugging.
Troubleshooting common issues in Puppeteer will be a simple task if you keep these suggestions in mind.
Happy Web Scraping and don't forget to prepare your web scraping script for the further deployment to server or cloud ☁️