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UnhandledPromiseRejectionWarning: ReferenceError: browser is not defined when running puppeteer?

Am new to using puppeteer and i want to scrape some data of of a certain website but i get these warnings and i get no data displayed on console.

Why do I get the following warnings, and how can I get rid of them?

Here is the code i used :

const puppeteer = require("puppeteer");
(async () => {
  // prepare for headless chrome
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  // set user agent (override the default headless User Agent)
  await page.setUserAgent(
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36"
  // go to website home page
  await page.goto("https://www.nytimes.com/");
  await page.waitForSelector("body");
  // get the User Agent on the context of Puppeteer
  const userAgent = await page.evaluate(() => navigator.userAgent);
  var rposts = await page.evaluate(() => {
    postItems = [];
    let posts = document.body.querySelectorAll(".assetWrapper");
    posts.forEach((item) => {
      try {
        title = item.querySelector("h2").innerText;
        link = item.querySelector("a").href;
        summary = item.querySelector("p").innerText;
        postItems.push({ title: title, link: link, summary: summary });
      } catch (e) {}
    var items = {
      posts: postItems,
    return items;
  // If everything correct then no 'HeadlessChrome' sub string on userAgent
  console.log(userAgent);
  console.log(rposts);
  await browser.close();
})();
here are the errors am getting : 
(node:4072) UnhandledPromiseRejectionWarning: ReferenceError: browser is not defined
(node:15452) UnhandledPromiseRejectionWarning: ReferenceError: Cannot access 'page' before initialization
Create browser with headless, then you can work with those code.
    const browser = await puppeteer.launch({
        headless: false
Regards,
        
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