Use page.evaluate(fn, ...args) to run a function in the current page, page.evaluateOnNewDocument(fn, ...args) to install code before a new document’s page scripts run, and page.exposeFunction(name, fn) when browser JavaScript needs to call back into Node.js. These APIs cross execution contexts: a function evaluated in the page does not inherit Node.js variables from its surrounding scope, so pass the values it needs as arguments.
Run a function in the current page
page.evaluate() evaluates a function in the page’s context and returns its result. Pass a function callback, followed by any values it needs:
const result = await page.evaluate((selector) => {
return document.querySelector(selector)?.textContent?.trim() ?? null;
}, '#headline');The callback can use browser-page objects such as document. If it returns a Promise, Puppeteer waits for that Promise to resolve before returning the result to Node.js. The example returns trimmed text from the matching element, or null if there is no match.
Pass Node.js values into the page function
The callback is serialized and run in the browser context; it does not close over Node.js lexical scope. A variable defined in your Node.js module is not automatically available inside the evaluated function. Pass it explicitly instead of interpolating it into source text:
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- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
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const prefix = 'Result: ';
const result = await page.evaluate((selector, prefix) => {
return prefix + (document.querySelector(selector)?.textContent ?? '');
}, '#headline', prefix);The arguments after the callback are passed to it in order. Keep the callback self-contained apart from those arguments and browser APIs. This makes the execution-context boundary visible and avoids creating dynamic JavaScript source strings.
Install code before page scripts run
Use page.evaluateOnNewDocument(fn, ...args) for setup that must happen after a document is created but before the page’s scripts execute. Register the hook before navigating to the page you want it to affect:
await page.evaluateOnNewDocument((language) => {
Object.defineProperty(navigator, 'language', { get: () => language });
}, 'en-US');
await page.goto(url);This is a lifecycle hook, not a way to change a document that has already loaded. The hook also runs for new documents created by navigation and for child frames when they attach or navigate. Supply values the function needs as arguments, just as you would with page.evaluate().
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- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
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- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Let page JavaScript call a Node.js function
Evaluation sends a function from Node.js into the page. For the reverse direction—page JavaScript calling a function handled by Node.js—use page.exposeFunction(name, fn):
await page.exposeFunction('lookupRecord', async (id) => {
return await getRecordFromNode(id);
});
const record = await page.evaluate(() => window.lookupRecord('item-42'));Puppeteer adds the exposed function to the page’s window. Calls from the page return a Promise that resolves with the Node.js function’s result. In this example, getRecordFromNode remains in the Node.js process; it is not copied into the page. The exposed function survives navigation, so page code can call it in a later document too.
Choose the API by timing and call direction
| What you need | API | When it runs and where data goes |
|---|---|---|
| Run an operation in the current page | page.evaluate(fn, ...args) |
Runs in the page context now; returns the result to Node.js and waits for a returned Promise. |
| Set up each new document before its scripts | page.evaluateOnNewDocument(fn, ...args) |
Runs after document creation and before page scripts, including for new documents on navigation and child-frame attachment or navigation. |
| Have browser JavaScript call Node.js | page.exposeFunction(name, fn) |
Creates a page-side function whose call is handled by Node.js and whose result is returned through a Promise. |
Why a function callback is safer than a source string
Puppeteer serializes function callbacks using their string representation. That means a callback must be valid when serialized and executed in the page; it cannot rely on Node.js lexical scope. Prefer a callback plus explicit arguments over assembling JavaScript source text yourself. It is easier to see what crosses the boundary and avoids quoting and escaping mistakes.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
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- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Transpilation can change the generated function form in ways that are incompatible with evaluation. That is a compatibility risk, not a guarantee that every transpiler will fail. If an evaluated callback breaks only in a transpiled build, inspect the function form Puppeteer receives and try a simple, untransformed callback to isolate the issue.
Common errors and fixes
“Cannot evaluate a string with arguments”
Arguments are passed to a function callback, not appended to a string of source code. Replace a string-based evaluation with a callback and pass values after it:
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsconst value = await page.evaluate((name) => {
return document.querySelector(name)?.textContent ?? null;
}, '#headline');A Node.js variable is undefined in the page
The evaluated callback runs in the browser context and does not inherit variables from Node.js. Add each needed value to the callback’s parameter list and pass it after the callback. If page code needs to invoke a Node.js operation, expose that operation with page.exposeFunction() instead.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
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- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
The setup ran too late
evaluateOnNewDocument() affects new documents; it does not retroactively run before scripts in a page that is already loaded. Register it before the relevant page.goto() or other navigation.
An evaluated function fails after transpilation
Puppeteer evaluates a serialized function, so generated output can matter. Inspect the callback Puppeteer receives, then test with a straightforward untransformed callback. If that works, adjust the build or callback form rather than assuming all transpiled functions are unsupported.
The page’s Content Security Policy blocks the needed operation
First check whether ordinary evaluation already does what you need; bypassing CSP is not the default injection method. If you specifically need CSP bypass, set page.setBypassCSP(true) before navigating to the domain, because bypass takes effect at CSP initialization.
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Or skip the browser setup
If your goal is to capture a page rather than run custom Puppeteer logic, ScreenshotNeo can return a screenshot or PDF from one GET request. For example, this saves a WebP screenshot of Stripe:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. Before capture, it accepts cookie or consent banners like a visitor and removes more than 60 known consent platforms, newsletter popups and chat widgets; each of those steps can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads and cache hits cost nothing, and response headers report the page verdict and whether the request was billed. Its MCP server provides take_screenshot, get_page_info and capture_pdf for AI agents using Claude, Cursor or another MCP client.
The Free plan includes 1,000 screenshots per month with no card. Paid plans start at $5 for 3,000 shots; every feature is available on every plan. Sign up free for 1,000 screenshots a month, with no card.
Frequently Asked Questions
Does page.evaluate() wait for an asynchronous callback?
Yes. If the callback returns a Promise, Puppeteer waits for it to resolve before returning the result.
The Tool Desk
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Will page.exposeFunction() still be available after navigation?
Yes. The exposed function survives navigation.
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