How to fix Puppeteer 'Error: Unknown key: "tab"'

Problem:

You want to emulate a tab key press using

await page.keyboard.press("tab");

but you get an error message like

(node:30594) UnhandledPromiseRejectionWarning: Error: Unknown key: "tab"
    at assert (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:270:11)
    at Keyboard._keyDescriptionForString (/home/uli/dev/myproject/node_modules/puppeteer/lib/Input.js:96:5)
    at Keyboard.down (/home/uli/dev/myproject/node_modules/puppeteer/lib/Input.js:44:30)
    at Keyboard.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:112:23)
    at Keyboard.press (/home/uli/dev/myproject/node_modules/puppeteer/lib/Input.js:178:16)
    at Keyboard.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:112:23)
    at /home/uli/dev/myproject/test.js:8:23
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
(node:30594) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:30594) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Solution

You need to use Tab, not tab ! The T needs to be uppercase!

Use

await page.keyboard.press("Tab");

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch({defaultViewport: {width: 1920, height: 1080}});
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Press tab 10 times (effectively scrolls down on techoverflow.net)
  for (let i = 0; i < 10; i++) {
      await page.keyboard.press("Tab");
  }
  // Screenshot to verify result
  await page.screenshot({path: 'screenshot.png'});
  // Cleanup
  await browser.close();
})();