Use Playwright’s page.addScriptTag() to run custom JavaScript after a page loads, or page.addInitScript() to install code after document creation but before the site’s scripts run. Then capture the result with page.screenshot(). Choose the injection timing based on what your script needs to change, and wait for the page to reach the state you intend to capture.
What custom JavaScript can do before a screenshot
Custom JavaScript lets an automated browser change or inspect a page before taking a screenshot. Typical uses include setting a page marker, changing a visible state, dismissing an element for a test, or preparing a page-specific condition. The capture reflects the browser state after your script has run; it does not guarantee that a site’s asynchronous content, animations, or other dynamic behavior has settled.
The two main Playwright injection methods differ in timing:
page.addScriptTag()adds JavaScript to a page context, commonly after navigation. Use it when the document is already available and the target change can happen afterward.page.addInitScript()runs after the document is created but before the page’s own scripts. Use it when site scripts may otherwise overwrite or prevent the state you want to set. It also runs for newly attached or navigated child frames.
Neither method makes arbitrary changes work on every website. Results depend on the site, the page state, frames, authentication, and browser behavior.
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Set up Playwright and capture a page
Install Playwright in a Node.js project, then install its Chromium browser. The example below is illustrative: adapt the URL, script, readiness condition, and output path to your target.
- Initialize a project and install Playwright:
npm init -y, thennpm install playwright. - Install Chromium with
npx playwright install chromium. - Save the following as
capture.jsand run it withnode capture.js.
const { chromium } = require('playwright');
(async () => {
const browser = await chromium.launch();
try {
const page = await browser.newPage();
await page.goto('https://example.com', { waitUntil: 'load' });
await page.addScriptTag({
content: `document.documentElement.dataset.captureReady = 'true';`
});
await page.screenshot({ path: 'capture.png', fullPage: true });
} finally {
await browser.close();
}
})();The script sets a data attribute on the document element; it is an example of a page-context change, not a requirement for screenshotting. Replace the URL and script with the page and change you actually need. The official Playwright Page API documents injection and screenshot options.
Choose the right injection timing
Run code after navigation with addScriptTag
Use page.addScriptTag() when the page has loaded far enough for your script to find its target. Playwright supports adding a script from inline content or a file path. For example, a local script can be injected with await page.addScriptTag({ path: 'capture-setup.js' }). Keep the injection after navigation if it depends on page elements that do not exist before the document loads.
Be deliberate about readiness. A navigation event such as load does not prove that every application-specific request or lazy-loaded section is complete. If the change depends on a particular element, wait for that element before injecting:
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await page.goto('https://example.com', { waitUntil: 'domcontentloaded' });
await page.locator('#main-content').waitFor();
await page.addScriptTag({ content: `
document.documentElement.dataset.captureReady = 'true';
` });
await page.screenshot({ path: 'capture.png', fullPage: true });Use a selector that identifies the state relevant to your page rather than assuming a fixed delay will work everywhere.
Run code before the site’s scripts with addInitScript
When page scripts need to see a value from the beginning, register an init script before navigating:
const { chromium } = require('playwright');
(async () => {
const browser = await chromium.launch();
try {
const page = await browser.newPage();
await page.addInitScript(() => {
window.captureMode = true;
});
await page.goto('https://example.com');
await page.screenshot({ path: 'capture.png', fullPage: true });
} finally {
await browser.close();
}
})();Playwright documents that init scripts run after document creation and before the page’s scripts. They are also evaluated in child frames when those frames are attached or navigated. This makes the method useful for early setup, but it does not guarantee that a site will use the value or that all frame behavior will match your expectations. Avoid putting secrets in page-context code.
Configure the screenshot itself
Playwright’s screenshot method can capture the viewport or the full scrollable page. Select options to match the output you need rather than assuming one capture mode fits every page.
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- Full page: set
fullPage: trueto capture the full page rather than only the current viewport. - Output format: choose PNG, JPEG, or WebP through the output path or screenshot options documented by Playwright. Match the format to the next step in your workflow.
- Scale: choose CSS-pixel or device-pixel scaling when output dimensions matter.
- Masking: mask matching locators to obscure changing or sensitive regions in the screenshot.
- Stylesheet override: apply a stylesheet during capture when you need a controlled visual adjustment without making a persistent site change.
These controls shape the output; they do not automatically stabilize dynamic content. If a page animates, loads images lazily, or changes after a request completes, define an appropriate wait or page-specific preparation step before capturing.
Use another integration when it fits better
Playwright is a high-level browser automation option, but it is not the only route. The right choice depends on whether you are writing a browser automation script, working directly with the browser protocol, or building an extension.
| Approach | Best fit | Injection and capture route |
|---|---|---|
| Playwright | Page-level JavaScript browser automation | Use addScriptTag() or addInitScript(), then page.screenshot(). Official Page API. |
| Puppeteer | High-level JavaScript automation with Chrome or Firefox | Puppeteer supports browser automation tasks including screenshots and PDFs. See the Puppeteer overview for its scope. |
| Chrome DevTools Protocol (CDP) | Direct, lower-level browser protocol control | Use Page.addScriptToEvaluateOnNewDocument for scripts in frames before their scripts load, and Page.captureScreenshot to capture. See the CDP Page domain. |
| Chrome extension scripting | Injection managed by a Chrome extension | Chrome’s scripting API injects JavaScript or CSS into websites. Its documented default timing is document_idle, or immediate execution if the page has already loaded. See the Chrome scripting API. |
These interfaces operate at different integration levels; the documentation does not establish one universally superior method. Use Playwright or Puppeteer for a library-driven automation workflow, CDP when you need protocol-level commands, and extension scripting when the behavior belongs in an extension.
Troubleshoot common capture failures
The script runs but the screenshot looks unchanged
Check that your code targets the correct element and executes in the intended frame. If the site changes the same state afterward, run the script later or move setup that must precede site code into addInitScript(). Verify the condition in the page before taking the screenshot.
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The script cannot find an element
The page may not have rendered the target yet, or the selector may not match the active page. Wait for a meaningful locator before injection. For content inside a frame, identify and work with that frame rather than assuming the top-level document contains the element.
The screenshot is incomplete or inconsistent
A navigation lifecycle event may occur before the content you care about is ready. Wait for a target selector or application-specific state. Full-page capture can include content beyond the viewport, but does not by itself promise that lazy images or other delayed content have finished loading.
The page behaves differently under automation
Sites can vary behavior based on browser context, login state, frames, or security controls. The cited APIs document injection capabilities, not successful modification of every site. Reproduce the needed authentication and browser conditions, and avoid assuming a script will bypass site security or access restrictions.
The process leaves a browser open after an error
Put browser shutdown in a finally block, as in the examples, so the browser is closed even if navigation, injection, or capture throws an error. Log or surface the original error as needed rather than silently treating a failed capture as a valid image.
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Performance, reliability, and cost considerations
A local Playwright workflow gives you control over browser launch, page context, injection timing, and capture settings. That control also means you manage browser installation, script failures, readiness logic, and output storage. A single fixed delay can make a script unnecessarily slow on quick pages and still too short on slow ones; a meaningful selector or state condition is generally more specific to the capture you need.
For recurring or large batches, consider how your own system will handle browser startup, timeouts, retries, and failures. The official API references describe available capabilities but do not establish a universal success rate, runtime, or cost for your target sites. Measure your own pages and workload before relying on a particular configuration.
Or skip the browser setup
ScreenshotNeo is a website screenshot API and MCP server for developers. Instead of installing and managing a browser for a straightforward capture, send one GET request with the target URL. Its JavaScript option can run custom code before capture; the API also supports PNG, JPEG, WebP, and PDF output. See the ScreenshotNeo documentation for parameters and setup.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpScreenshotNeo accepts cookie or consent banners like a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; each step can be turned off. Bot checks and CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report the page verdict and billing status. Its MCP server provides take_screenshot, get_page_info, and capture_pdf tools for AI agents and MCP clients. The free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000 shots.
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Frequently asked questions
Can custom JavaScript make a screenshot capture a logged-in page?
The injection APIs do not themselves provide authentication. A capture must run in a browser context with the required login state and permissions.
Does full-page capture guarantee every lazy-loaded image appears?
No. Full-page mode selects the capture extent; it does not promise every delayed asset has loaded. Add page-specific readiness handling where needed.
Should I use Playwright or CDP?
Use Playwright for page-level automation through a library API. Use CDP when you need direct browser protocol commands. Their documented capabilities do not make either choice universally best.
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