JavaScript can capture either a reconstruction of page content or the actual pixels of a browser tab, window, or monitor. Use html2canvas when you need an element or document rendered from readable DOM and CSS; use navigator.mediaDevices.getDisplayMedia() when the user must choose a display surface. Neither method is a universal replacement for the other, and both have important security and fidelity limits.
Choose the right kind of screenshot
Start by defining what “screenshot” means in your application:
| Requirement | Best fit | What it captures | Important limitation |
|---|---|---|---|
| An element, component, or page content | html2canvas |
A canvas reconstruction of readable DOM and supported CSS | It is not a pixel-level browser screenshot; unsupported CSS, cross-origin images, and cross-origin iframes can differ or fail |
| A selected tab, window, monitor, or other display surface | getDisplayMedia() |
Video frames from the surface the user selects | Requires a secure context, user interaction, permission, and a browser chooser; browser support is limited |
| A server-side image or PDF from a URL | ScreenshotNeo | A clean rendered page returned by an API | Requires an API key and an HTTP request rather than running entirely in the visitor’s browser |
The choice affects permissions, cross-origin behavior, fidelity, performance, and whether browser chrome or another application can appear in the result.
Capture an HTML element with html2canvas
html2canvas walks the target DOM, reads styles and resources available to the page, and paints a representation into a canvas. Load it in your page, select an element, and wait for the returned promise.
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Basic element capture
<button id="save-card">Save card</button>
<article id="capture">
<h1>Monthly report</h1>
<p>Revenue increased 18% this quarter.</p>
</article>
<script src="https://cdn.jsdelivr.net/npm/html2canvas@1.4.1/dist/html2canvas.min.js"></script>
<script>
document.querySelector('#save-card').addEventListener('click', async () => {
const element = document.querySelector('#capture');
const canvas = await html2canvas(element);
canvas.toBlob((blob) => {
if (!blob) throw new Error('The canvas could not be exported.');
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'monthly-report.png';
link.click();
URL.revokeObjectURL(url);
}, 'image/png');
});
</script>The promise resolves to an HTMLCanvasElement. Appending that canvas to the document is a useful debugging step:
html2canvas(document.querySelector('#capture')).then((canvas) => {
document.body.appendChild(canvas);
});Capture the entire document
Passing document.body captures the body’s rendered content as reconstructed by the library. For long pages, explicitly provide the document dimensions so the canvas is not limited to the current viewport:
const width = Math.max(
document.body.scrollWidth,
document.documentElement.scrollWidth,
document.documentElement.clientWidth
);
const height = Math.max(
document.body.scrollHeight,
document.documentElement.scrollHeight,
document.documentElement.clientHeight
);
const canvas = await html2canvas(document.body, {
width,
height,
windowWidth: width,
windowHeight: height,
scale: window.devicePixelRatio
});
canvas.toBlob((blob) => {
if (!blob) return;
const link = document.createElement('a');
link.href = URL.createObjectURL(blob);
link.download = 'full-page.png';
link.click();
}, 'image/png');Very large pages can consume substantial memory. Consider capturing sections separately, lowering scale, or exporting with toBlob() rather than creating a giant data URL.
Region, scale, and image options
x,y,width, andheightrestrict rendering to a region.scale: window.devicePixelRatiomakes output sharper on high-density displays, but increases pixel count and memory use. A fixed value such as1is more predictable for large exports.useCORS: trueallows images that explicitly grant cross-origin access through CORS headers. It cannot bypass the browser’s same-origin policy.- Use
onclonewhen you need to alter the cloned document—for example, hide a button or reveal a print-only section without changing the live page.
const canvas = await html2canvas(document.querySelector('#invoice'), {
backgroundColor: '#ffffff',
scale: 2,
useCORS: true,
x: 0,
y: 0,
width: 900,
height: 700,
onclone: (clonedDocument) => {
clonedDocument.querySelector('.download-button')?.remove();
}
});Export the canvas as PNG, JPEG, or WebP
Use toBlob() for downloads and uploads
toBlob() avoids turning the entire image into a large in-memory string. The callback receives a Blob, or null if encoding fails.
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function downloadCanvas(canvas, filename, type = 'image/png', quality) {
canvas.toBlob((blob) => {
if (!blob) {
console.error('Canvas encoding failed');
return;
}
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.download = filename;
link.href = url;
link.click();
setTimeout(() => URL.revokeObjectURL(url), 1000);
}, type, quality);
}
// PNG is lossless; quality is ignored by most browsers.
downloadCanvas(canvas, 'capture.png', 'image/png');
// JPEG and WebP accept a quality number from 0 to 1 where supported.
downloadCanvas(canvas, 'capture.jpg', 'image/jpeg', 0.9);Use toDataURL() only when a data URL is useful
canvas.toDataURL() returns a data URL and defaults to PNG when the type is omitted or unsupported:
const dataUrl = canvas.toDataURL('image/png');
previewImage.src = dataUrl;Because the complete encoded image is held in a JavaScript string, toDataURL() can create memory and URL-length problems for large captures. Prefer toBlob() for downloads, uploads, and storage.
Capture the actual screen, window, or tab
The Screen Capture API’s navigator.mediaDevices.getDisplayMedia() asks the user to choose a monitor, window, or tab. It returns a MediaStream, not an image. Draw one video frame to a canvas after metadata is available, then export it.
Complete still-image example
<button id="share-screen">Choose a surface</button>
<video id="preview" autoplay muted playsinline hidden></video>
<script>
const button = document.querySelector('#share-screen');
const video = document.querySelector('#preview');
button.addEventListener('click', async () => {
let stream;
try {
stream = await navigator.mediaDevices.getDisplayMedia({
video: { displaySurface: 'browser' },
audio: false
});
video.srcObject = stream;
await video.play();
await new Promise((resolve) => {
if (video.readyState >= 2) resolve();
else video.addEventListener('loadeddata', resolve, { once: true });
});
const canvas = document.createElement('canvas');
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
canvas.getContext('2d').drawImage(video, 0, 0);
canvas.toBlob((blob) => {
if (!blob) return;
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'display-capture.png';
link.click();
URL.revokeObjectURL(url);
}, 'image/png');
} catch (error) {
if (error.name === 'NotAllowedError') {
console.warn('The user denied capture or cancelled the chooser.');
} else {
console.error('Display capture failed:', error);
}
} finally {
stream?.getTracks().forEach((track) => track.stop());
video.srcObject = null;
}
});
</script>Requirements and permission behavior
- Serve the page from a secure context (normally HTTPS; localhost is treated specially during development).
- Start the call from a recent user interaction such as a button click. Do not trigger it silently on page load.
- The browser displays its own chooser and permission UI. JavaScript cannot select a particular monitor or window without the user.
- Always stop the stream’s tracks after taking the still image, especially in a long-lived single-page application.
- Test your target browser matrix: MDN marks
getDisplayMedia()as limited availability, and some widely used browsers do not support it.
The selected surface can include content outside your page, but browser chrome and protected content may be excluded by the browser. The exact choices and restrictions are browser-controlled.
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Why html2canvas misses images or styles
Cross-origin images
An image hosted on another origin must send suitable CORS headers for the browser to expose its pixels. Set useCORS: true only when the image server permits it. If a cross-origin image is drawn without permission, the canvas becomes tainted and calls such as toBlob() or toDataURL() can fail with a security error. A server-side proxy that fetches and serves the image from your origin is the usual alternative, subject to that site’s policies.
Cross-origin iframes
Scripts on your page cannot inspect or reconstruct the DOM of an iframe from another origin. html2canvas therefore cannot reliably render its contents. Capture the iframe’s own page from code running there, obtain cooperation through an appropriate postMessage design, or use a server-side browser capture.
Unsupported or complex CSS
html2canvas implements a renderer for many common properties; it does not ask the browser for its final pixels. Filters, blend modes, pseudo-elements, video frames, fonts that have not loaded, and newer CSS features can therefore differ from the visible page. Wait for fonts and images before capturing:
await document.fonts.ready;
await Promise.all([...document.images].map((image) => {
if (image.complete) return Promise.resolve();
return new Promise((resolve) => {
image.addEventListener('load', resolve, { once: true });
image.addEventListener('error', resolve, { once: true });
});
}));
const canvas = await html2canvas(document.querySelector('#capture'));Performance, fidelity, and reliability decisions
- Pixel fidelity: display capture records the selected surface’s video frame. html2canvas is a DOM/CSS reconstruction and can be visually different even when the page looks correct.
- Permissions: element capture normally needs no prompt; display capture always depends on user selection and permission.
- Output size: increasing
scaleimproves detail but multiplies canvas pixels. UsetoBlob()and release object URLs. - Timing: capture after fonts, images, lazy-loaded content, animations, and data updates have settled. Disable animations in a cloned document when deterministic output matters.
- Security: same-origin policy protects cross-origin images and frames. No JavaScript option can legitimately override it.
- Browser coverage: canvas export is broadly available; Screen Capture API support varies substantially, so feature-detect it before showing the control.
const canShareDisplay = !!navigator.mediaDevices?.getDisplayMedia;
shareButton.hidden = !canShareDisplay;Troubleshooting checklist
“Permission denied” or no chooser appears
- Move the call into a click or keyboard handler.
- Use HTTPS (or localhost for local development).
- Check that the user did not cancel the chooser and that browser or enterprise policy does not disable screen sharing.
“SecurityError” when exporting
Find cross-origin images in the target tree. Configure the image host for CORS and use useCORS: true, remove the image from the capture, or render through a permitted proxy. Cross-origin iframe content cannot be read by the parent page.
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The screenshot is blank or only partly rendered
- Wait for
document.fonts.ready, image completion, and asynchronous data. - Ensure the target is not
display:noneand has non-zero dimensions. - For a long document, set explicit dimensions and inspect for fixed-position elements or lazy loading that only occurs after scrolling.
The result looks different from the page
That is expected when unsupported CSS, web fonts, video, filters, or cross-origin resources are involved. Use getDisplayMedia() when the requirement is the visible display, or move rendering to a browser automation/API service.
The display image has the wrong dimensions
Use the video’s intrinsic videoWidth and videoHeight for the canvas, not CSS dimensions. Drawing before loadeddata or before a frame is available can produce an empty image.
Or skip the browser setup
For a URL you control or need to capture from a backend, ScreenshotNeo provides a single HTTP request that returns PNG, JPEG, WebP, or PDF. It accepts the cookie or consent banner like a visitor, then removes more than 60 known consent platforms, newsletter popups, and chat widgets; each cleanup step can be disabled. Only clean shots are billed: bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report the page verdict and billing status.
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Which method should you ship?
- Choose html2canvas for user-requested snapshots of your own DOM when a close reconstruction is acceptable.
- Choose
getDisplayMedia()for a user-selected tab, window, or monitor and design around its permission and compatibility requirements. - Choose ScreenshotNeo when you need repeatable URL capture, server-side processing, clean pages, PDFs, automation controls, or AI-agent access without building a browser-capture flow.
Frequently Asked Questions
Can JavaScript capture browser tabs without asking the user?
No. A browser must show the getDisplayMedia() chooser and obtain permission. Silent tab or monitor capture is intentionally blocked.
Can html2canvas capture a cross-origin iframe?
Not from the parent page. Same-origin policy prevents reading another origin’s iframe DOM; the iframe application or a server-side capture must handle it.
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Should I use PNG or JPEG for a screenshot?
PNG is lossless and the default. JPEG can be smaller for photographic content and accepts a quality value, while text-heavy UI usually remains clearer in PNG.
Why does my canvas export throw a security error?
A cross-origin image without successful CORS authorization likely tainted the canvas. Configure CORS, use an approved proxy, or omit that resource.
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