Puppeteer: Session closed. Most likely the page has been closed.

Each page has its own DevTools session. When the page is closed, or the browser exits, that session is detached, and any command sent afterwards is rejected with this message. The method in parentheses is the command that was attempted, for example Runtime.callFunctionOn for an evaluate or Page.navigate for a goto.

In practice the page was closed by your own code or by the browser crashing. Missing await keywords are the classic cause: a function returns, browser.close() runs in a finally block, and an un-awaited page.evaluate() fails a moment later. Pages that call window.close() (OAuth popups) and memory-starved containers that kill renderer processes produce the same error.

What is not wrong: the evaluated code or selector. The target simply no longer exists.

const browser = await puppeteer.launch();
try {
  const page = await browser.newPage();
  page.on('close', () => console.warn('page closed'));
  await page.goto('https://example.com/');
  const title = await page.evaluate(() => document.title); // awaited
  console.log(title);
} finally {
  await browser.close();
}

Structure scripts so the browser's lifetime visibly encloses every call, usually with try/finally and awaited calls only. Isolate concurrent work in separate pages or contexts. Monitor memory in containers, since renderer crashes show up as closed sessions rather than as obvious out-of-memory errors.