How do I pause execution until a JavaScript function completes when scraping with Puppeteer/Node.js?

Other Questions Puppeteer
1

I need to wait for a JavaScript function to finish executing before interacting with dynamic elements using Puppeteer. How can I ensure this evaluation completes?

console.log('Starting page load...');
await webPage.goto('https://example.com', { waitUntil: 'domcontentloaded' });

console.log('Initiating process...');
await webPage.waitForSelector('#launch-btn', { visible: true });
await webPage.click('#launch-btn');

console.log('Waiting for process completion...');
await webPage.waitForFunction(() => window.taskDone === true, { timeout: 40000 });
console.log('Process finished, proceeding...');
2

hey, have u tried ensuring the func returns a boolean? sometimes a tiny delay or slight adjustmnt in the condition fixes it. also, a try/catch might help dbg errors. good luck!

3

Based on my experience, leveraging waitForFunction is a solid strategy to ensure your JavaScript process completes before proceeding in Puppeteer. It is crucial to confirm that the condition within waitForFunction actually reflects what you expect from your dynamic elements. I encountered an issue where timing mismatches between script execution and DOM updates led to intermittent failures. Adjusting the function to properly signal completion, perhaps by using a promise, helped resolve the issue. Additionally, reviewing the page’s JavaScript to ensure the flag sets accurately can prevent unexpected results.

4

I’ve dealt with a similar issue when working on a dynamic site. I found that the root of the problem was often related to how and when the flag or condition variable was updated. In my case, rather than solely relying on waitForFunction, I combined it with a page.evaluate() call to check the variable’s state when I thought it should have changed. This helped pinpoint timing discrepancies between the Puppeteer script and the page’s own JavaScript. Ensuring that the flag is reliably set in the page’s context before moving forward was ultimately the key to a robust solution.