The waitForFunction can be used to observe viewport size change:

const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
const watchDog = page.waitForFunction('window.innerWidth < 100');
await page.setViewport({ width: 50, height: 50 });
await watchDog;
await browser.close();
})();

To pass arguments from node.js to the predicate of page.waitForFunction function:

const selector = '.foo';
await page.waitForFunction(
(selector) => !!document.querySelector(selector),
{},
selector
);

The predicate of page.waitForFunction can be asynchronous too:

const username = 'github-username';
await page.waitForFunction(
async (username) => {
const githubResponse = await fetch(
 `https://api.github.com/users/${username}`
);
const githubUser = await githubResponse.json();
// show the avatar
const img = document.createElement('img');
img.src = githubUser.avatar_url;
// wait 3 seconds
await new Promise((resolve, reject) => setTimeout(resolve, 3000));
img.remove();
},
{},
username
);