How to select elements within an iframe element in Puppeteer

You can get the iframe using contentFrame as you are doing now, and then call $.

const browser = await puppeteer.launch({ headless: false });
const page = await browser.newPage();

await page.goto('http://www.espn.com/login')

const elementHandle = await page.waitForSelector('div#disneyid-wrapper iframe');
const frame = await elementHandle.contentFrame();
await frame.waitForSelector('[ng-model="vm.username"]');
const username = await frame.$('[ng-model="vm.username"]');
await username.type('foo');
await browser.close()

I had an issue with finding stripe elements. The reason for that is the following:

You can't access an with different origin using JavaScript, it would be a huge security flaw if you could do it. For the same-origin policy browsers block scripts trying to access a frame with a different origin. See more detailed answer here

Therefore when I tried to use puppeteer's methods:Page.frames() and Page.mainFrame(). ElementHandle.contentFrame() I did not return any iframe to me. The problem is that it was happening silently and I couldn't figure out why it couldn't find anything.

Adding these arguments to launch options solved the issue: '--disable-web-security', '--disable-features=IsolateOrigins,site-per-process'