Core concepts

Playwright provides a set of APIs to automate Chromium, Firefox and WebKit browsers. By using the Playwright API, you can write JavaScript code to create new browser pages, navigate to URLs and then interact with elements on a page.

Along with a test runner Playwright can be used to automate user interactions to validate and test web applications. The Playwright API enables this through the following primitives.

Browser
Browser contexts
Pages and frames
Selectors
Auto-waiting
Execution contexts
Object & element handles

Browser

A Browser refers to an instance of Chromium, Firefox or WebKit. Playwright scripts generally start with launching a browser instance and end with closing the browser. Browser instances can be launched in headless (without a GUI) or headful mode.

const { chromium } = require('playwright');  // Or 'firefox' or 'webkit'.

const browser = await chromium.launch({ headless: false });
await browser.close();

Launching a browser instance can be expensive, and Playwright is designed to maximize what a single instance can do through multiple browser contexts.

Browser contexts

A BrowserContext is an isolated incognito-alike session within a browser instance. Browser contexts are fast and cheap to create. Browser contexts can be used to parallelize isolated test executions.

const browser = await chromium.launch();
const context = await browser.newContext();

Browser contexts can also be used to emulate multi-page scenarios involving mobile devices, permissions, locale and color scheme.

const { devices } = require('playwright');
const iPhone = devices['iPhone 11 Pro'];

const context = await browser.newContext({
  ...iPhone,
  permissions: ['geolocation'],
  geolocation: { latitude: 52.52, longitude: 13.39},
  colorScheme: 'dark',
  locale: 'de-DE'
});

Pages and frames

A Browser context can have multiple pages. A Page refers to a single tab or a popup window within a browser context. A page can be used to navigate to URLs and then interact with elements.

const page = await context.newPage();
await page.goto('http://example.com');
await page.click('#submit');

A page can have one or more Frame objects attached to it. Each page has a main frame and page-level interactions (like click) are assumed to operate in the main frame.

A page can have additional frames attached with the iframe HTML tag. These frames can be accessed for interactions inside the frame.

// To interact with elements in an iframe
const frame = page.frame('frame-name');
await frame.fill('#username-input');

Selectors

Auto-waiting

Execution contexts

Playwright scripts run in your Node.js environment. You page scripts run in the page environment. Those environments don't intersect, they are running in different virtual machines in different processes and potentially on different computers.

IMAGE PLACEHOLDER

The page.evaluate API can run a JavaScript function in the context of the web page and bring results back to the Node.js environment. Globals like window and document along with the web page runtime can be used in evaluate.

Right:

const data = { text: 'some data', value: 1 };
// Pass |data| as a parameter.
const result = await page.evaluate(data => {
  window.myApp.use(data);
}, data);

Wrong:

const data = { text: 'some data', value: 1 };
const result = await page.evaluate(() => {
  // There is no |data| in the web page.
  window.myApp.use(data);
});

Evaluation parameters are serialized and sent into your web page over the wire. You can pass primitive types, JSON-alike objects and remote object handles received from the page.

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