Question

Technologies:

javascript

node.js

Tolerim

20 days ago

Is it necessary to include error and pageerror handlers in puppeteer or is utilizing try/catch enough?

I'm unsure if it's necessary to add page listeners in Puppeteer to catch all errors. In the provided code snippet, handlers for the 'error' and 'pageerror' events have been included. But aren't these errors already being caught by the try/catch around await page.goto()? I'm wondering, what does the try/catch block catch that the handlers don't, and vice versa? If the handlers are reacting to uncaught exceptions, how can these errors be properly handled without causing an uncaughtException, since they happen outside of the normal async/await flow? My goal is to handle all errors in the same way, using the same error handling logic for all of them. Is it possible to await all errors and handle any error in the same way, instead of just a subset of them?

Enclosing your code in

tags is recommended if you're generating code, as the output written to an HTML file on the front end must comply with HTML syntax. Here is an example of creating a set of radio inputs with checkboxes that only allow for one selection at a time by utilizing the same name attribute for all checkboxes and setting their type attribute to "radio":

I hope this information helps! If you have any further questions, please let me know. Additionally, I have attempted to resolve this issue by wrapping everything in new Promise((resolve, reject) => { ... }) and utilizing reject(error) in the page error handlers. However, I'm still encountering some strange uncaughtException errors in my actual code (which I'm unable to reproduce in a simplified example). Do you have any insight into whether the new Promise() approach is correct in this context, or what the correct strategy would be?

Answers(2)

Tolerim

20 days ago

The try/catch block will catch errors that occur when executing the code inside it. However, the error and pageerror event listeners will catch errors that occur outside of the try/catch block, such as errors that occur during navigation or when trying to evaluate code in the page context. To handle all errors in a consistent way, you can use a combination of the try/catch block and the event listeners. You can log any errors caught by the event listeners and then re-throw them to be caught by the try/catch block. Here's an example:

(async () => {
  try {
    const browser = await puppeteer.launch({ headless: true, args: ['--no-sandbox'] });
    const page = await browser.newPage();

    // Catch errors with event listeners
    page.on('error', error => {
      console.error('Page on error:', error);
      throw error;
    });
    page.on('pageerror', error => {
      console.error('Page on pageerror:', error);
      throw error;
    });

    await page.goto('https://www.example.com');
    await page.screenshot({ path: './tmp/example.png' });
    await browser.close();
  } catch (err) {
    console.error('Try/catch error:', err);
  }
})();

In this example, we log any errors caught by the event listeners and then immediately re-throw them using throw error;. This allows them to be caught by the try/catch block and handled in a consistent way. Wrapping the code in a Promise and calling reject(error) in the event listeners can work as well, but you need to make sure that you are properly chaining the Promise with catch() to catch any errors that occur. Here's an example:

new Promise(async (resolve, reject) => {
  try {
    const browser = await puppeteer.launch({ headless: true, args: ['--no-sandbox'] });
    const page = await browser.newPage();

    // Catch errors with event listeners
    page.on('error', error => {
      console.error('Page on error:', error);
      reject(error);
    });
    page.on('pageerror', error => {
      console.error('Page on pageerror:', error);
      reject(error);
    });

    await page.goto('https://www.example.com');
    await page.screenshot({ path: './tmp/example.png' });
    await browser.close();

    resolve();
  } catch (err) {
    console.error('Try/catch error:', err);
    reject(err);
  }
}).catch(err => {
  console.error('Promise error:', err);
});

In this example, we wrap the code in a Promise, and call reject(error) in the event listeners to reject the Promise with the error that occurred. We also add a .catch() at the end to catch any errors that occur in the Promise chain, including any errors thrown by the event listeners.

Accepted Answer

The try/catch block around await page.goto() will catch any errors that occur during the navigation process. However, it won't catch errors that occur outside of the navigation process, such as errors that occur when you interact with the page. The 'error' and 'pageerror' events are used to catch these types of errors. If you want to handle all errors in the same way, you can create a function that takes an error object as an argument and handles it accordingly. You can then pass this function as a callback to both the 'error' and 'pageerror' events. This way, any error that occurs will be handled by the same function. Regarding your question about how to handle uncaught exceptions without causing an uncaughtException, one approach is to wrap your code in a try/catch block and use process.emitWarning() to emit a warning instead of throwing an error. You can then listen for this warning using the 'warning' event and handle it accordingly. As for your question about whether it's possible to await all errors and handle them in the same way, I'm afraid that's not possible. Errors are thrown synchronously, so you can't use await to catch them. Instead, you'll need to use a combination of try/catch blocks and event listeners to handle all possible errors. Regarding your code snippet, enclosing your code in

tags is indeed recommended if you're generating code. This ensures that the output complies with HTML syntax. Your example of creating a set of radio inputs with checkboxes is correct. By setting the same name attribute for all checkboxes and setting their type attribute to "radio", you ensure that only one checkbox can be selected at a time. I hope this helps! Let me know if you have any further questions.