To emulate a keypress to the Enter key in Puppeteer, use

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

The E needs to be uppercase for this to work!

In order to emulate a tab key press in Puppeteer, 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();
})();

Use this snippet to set the value of an HTML <input> element in Puppeteer:

const newInputValue = "test 123";
await page.evaluate(val => document.querySelector('.search-form-input').value = val, newInputValue);amp

Remember to replace '.search-form-input' by whatever CSS selector is suitable to select your <input>. Examples include 'input[name="username"]' or '.username > input'.

Full example:

// Minimal puppeteer example
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Set input value
  const newInputValue = "test 123";
  await page.evaluate(val => document.querySelector('.search-form-input').value = val, newInputValue);
  // Screenshot to verify result
  await page.screenshot({path: 'screenshot.png'});
  // Cleanup
  await browser.close();
})();

Note that this method will work for any simple <input>, however it might not work for some heavily Javascripted inputs which you can find on some modern websites.

Using Python (pyppeteer)? Check out Pyppetteer minimal network response interception example

This example shows you how to intercept network responses in puppeteer.

Note: This intercepts the response, not the request! This means you can abort the request before it is actually sent to the server, but you can’t read the content of the response! See Minimal puppeteer request interception example for an example on how to intercept requests.

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  // Enable response interception
  page.on('response', async (response) => {
      console.info("URL", response.request().url());
      console.info("Method", response.request().method())
      console.info("Response headers", response.headers())
      console.info("Request headers", response.request().headers())
      // Use this to get the content as text
      const responseText = await response.text();
      // ... or as buffer (for binary data)
      const responseBuffer = await response.buffer();
      // ... or as JSON, if it's a JSON (else, this will throw!)
      const responseObj = await response.json();
  })
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

Using Python (pyppeteer)? Check out Pyppetteer minimal network request interception example

This example shows you how to intercept network requests in puppeteer:

Note: This intercepts the request, not the response! This means you can abort the request made, but you can’t read the content of the response! See Minimal puppeteer response interception example for an example on how to intercept responses.

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  // Enable request interception
  await page.setRequestInterception(true);
  page.on('request', async (request) => {
      console.info("URL", request.url());
      console.info("Method", request.method())
      console.info("Headers", request.headers())
      return request.continue(); // Allow request to continue
      // return request.abort(); // use this instead to abort the request!
  })
  await page.goto('https://techoverflow.net', {waitUntil: 'domcontentloaded'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

Problem:

You are trying to set the viewport size in Puppeteer using

const browser = await puppeteer.launch({
    defaultViewport: '1920x1080'
});

but you see an error message like

(node:15692) UnhandledPromiseRejectionWarning: Error: Protocol error (Emulation.setDeviceMetricsOverride): Invalid parameters width: integer value expected; height: integer value expected
    at /home/uli/dev/myproject/node_modules/puppeteer/lib/Connection.js:183:56
    at new Promise (<anonymous>)
    at CDPSession.send (/home/uli/dev/myproject/node_modules/puppeteer/lib/Connection.js:182:12)
    at EmulationManager.emulateViewport (/home/uli/dev/myproject/node_modules/puppeteer/lib/EmulationManager.js:41:20)
    at Page.setViewport (/home/uli/dev/myproject/node_modules/puppeteer/lib/Page.js:808:54)
    at Page.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:112:23)
    at Function.create (/home/uli/dev/myproject/node_modules/puppeteer/lib/Page.js:49:18)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async Browser._createPageInContext (/home/uli/dev/myproject/node_modules/puppeteer/lib/Browser.js:177:18)
    at async /home/uli/dev/myproject/index.js:8:16
  -- ASYNC --
    at Target.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:111:15)
    at Browser._createPageInContext (/home/uli/dev/myproject/node_modules/puppeteer/lib/Browser.js:177:31)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async /home/uli/dev/myproject/index.js:8:16
  -- ASYNC --
    at Browser.<anonymous> (/home/uli/dev/myproject/node_modules/puppeteer/lib/helper.js:111:15)
    at /home/uli/dev/myproject/index.js:8:30
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
(node:15692) 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: 1)
(node:15692) [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

{defaultViewport: {width: 1920, height: 1080}}

instead of

{defaultViewport: '1920x1080'}

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'});
  // Make a screenshot
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();