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Wait for the Promise returned by html2canvas(element). When it fulfills, its value is the rendered <canvas>. Put export, display, or upload code after await, or in .then(); handle a rejected Promise separately. The old onrendered callback is not the current completion API.
The completion signal is Promise fulfillment
html2canvas reconstructs the target element from the DOM and resolves a Promise with a canvas. That fulfillment is the supported signal that this particular rendering call has produced an output you can consume.
async function captureElement(element) {
try {
const canvas = await html2canvas(element);
// This runs only after this html2canvas call has fulfilled.
return canvas;
} catch (error) {
// The rendering call rejected.
console.error('html2canvas failed:', error);
throw error;
}
}The Promise settles only for the invocation you made. It does not certify that every network request in your application has ended, that an animation has reached its final frame, or that the pixels exactly match a browser screenshot. html2canvas builds its own representation and supports only the CSS and browser features it understands.
What each signal means
| Signal | Meaning | Use it for completion? |
|---|---|---|
| Promise fulfillment | A canvas was produced for this call. | Yes. Continue with export or display. |
| Promise rejection | This call could not complete successfully. | Yes. Enter your failure path. |
onError option |
A resource failed while rendering; rendering can continue. | No. It is a resource notification, not a finished-render callback. |
onrendered |
Legacy callback from older examples. | No. Use the Promise API. |
Use async/await in modern code
An async function makes the ordering explicit. Everything after await html2canvas(...) runs after fulfillment, while catch handles a rejected Promise.
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import html2canvas from 'html2canvas';
async function downloadCard() {
const element = document.querySelector('#invoice-card');
if (!element) {
throw new Error('Invoice card was not found');
}
try {
const canvas = await html2canvas(element, {
backgroundColor: '#ffffff',
imageTimeout: 15000
});
const link = document.createElement('a');
link.download = 'invoice-card.png';
link.href = canvas.toDataURL('image/png');
link.click();
} catch (error) {
console.error('Could not create the image:', error);
// Show an error message or retry according to your application rules.
}
}
document.querySelector('#download').addEventListener('click', downloadCard);imageTimeout is 15,000 milliseconds by default. Setting it explicitly documents the behavior your capture expects; it does not make an inaccessible cross-origin image readable.
Use .then() when callbacks fit your code
The callback form waits on the same Promise and is equivalent to await. Always attach .catch() so a rejected render does not become an unhandled rejection.
const element = document.querySelector('#report');
html2canvas(element, { scale: 2 })
.then((canvas) => {
document.querySelector('#preview').replaceChildren(canvas);
return canvas.toBlob((blob) => {
if (blob) {
console.log('PNG blob is ready', blob.size, 'bytes');
}
}, 'image/png');
})
.catch((error) => {
console.error('Render rejected:', error);
});Do not put follow-up work immediately after the html2canvas call and assume it has finished:
const promise = html2canvas(element);
// This line runs before the Promise has fulfilled.
console.log('Capture started');Keep export, upload, or UI updates inside the fulfillment path.
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Prepare application state before calling html2canvas
Promise fulfillment covers html2canvas’s work, not arbitrary application readiness. If your page loads data, swaps images, applies fonts, or changes classes asynchronously, make those conditions explicit before starting the capture.
Wait for your own data and UI state
async function renderReadyReport() {
await reportStore.load();
await customElements.whenDefined('sales-report');
const report = document.querySelector('sales-report');
report.classList.add('capture-mode');
// Let layout and style changes reach a frame.
await new Promise(requestAnimationFrame);
return html2canvas(report);
}The exact readiness condition belongs to your application. For example, wait for the API request that supplies table rows, then wait for the component that displays them, then capture.
Check images and fonts when they matter
For images already in the document, you can wait for each element’s load or error state. A failed image should be handled deliberately rather than mistaken for a successful visual result.
function waitForImage(image) {
if (image.complete) {
return image.naturalWidth > 0
? Promise.resolve()
: Promise.reject(new Error(`Image failed: ${image.src}`));
}
return new Promise((resolve, reject) => {
image.addEventListener('load', resolve, { once: true });
image.addEventListener('error', () => reject(new Error(`Image failed: ${image.src}`)), { once: true });
});
}
async function captureWithAssets(element) {
await Promise.all([...element.querySelectorAll('img')].map(waitForImage));
if (document.fonts) {
await document.fonts.ready;
}
return html2canvas(element);
}This preparation prevents a race in your application; it does not remove browser security restrictions. Images served from another origin may require suitable CORS headers, and the project documents cross-origin limitations.
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Use onclone for capture-only changes
The options reference provides an onclone hook that receives the cloned document. It is useful for hiding controls, adding a print class, or freezing a visual state without changing the live page. The hook is a preparation hook, not a completion notification.
const canvas = await html2canvas(document.querySelector('#dashboard'), {
onclone: (clonedDocument) => {
clonedDocument.body.classList.add('capture-mode');
clonedDocument.querySelectorAll('.live-only').forEach((node) => {
node.style.display = 'none';
});
}
});A reliable end-to-end capture function
This pattern validates the target, waits for application assets, invokes html2canvas once, and returns only after a canvas exists.
async function capture(selector) {
const element = document.querySelector(selector);
if (!element) {
throw new Error(`No element matches ${selector}`);
}
await Promise.all([...element.querySelectorAll('img')].map(waitForImage));
if (document.fonts) {
await document.fonts.ready;
}
await new Promise(requestAnimationFrame);
try {
const canvas = await html2canvas(element, {
imageTimeout: 15000,
onclone: (doc) => doc.body.classList.add('capture-mode')
});
return canvas;
} catch (error) {
console.error(`html2canvas rejected for ${selector}:`, error);
throw error;
}
}Callers can now decide whether to display the canvas, call toBlob(), or send the resulting bytes to a server. Those operations belong after the returned Promise resolves.
Troubleshoot a render that appears not to finish
The Promise never appears to settle
- Confirm that the code actually calls
html2canvasand that the target is a real element, notnull. - Inspect the browser console for an exception thrown before the call or inside your own readiness code.
- Check large or unreachable resources. The default
imageTimeoutis 15 seconds; reduce the number of assets or set a timeout appropriate to your page. - Do not wait on a Promise that your application creates but never resolves. Log immediately before the html2canvas call and in both fulfillment and rejection handlers.
The Promise fulfills but the canvas is incomplete
Fulfillment proves that html2canvas produced a canvas, not that every visual dependency was available. Verify image load state, font readiness, data rendering, and the target’s computed styles before invoking the library. Cross-origin images can be omitted or taint the canvas when server permissions are not configured.
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You used onError as a finished callback
onError reports a resource failure while rendering continues. It can be useful for diagnostics, but the only place to run “done” logic is the Promise fulfillment branch. Keep a separate error counter if you want to warn about missing assets.
let failedResources = 0;
const canvas = await html2canvas(element, {
onError: (error) => {
failedResources += 1;
console.warn('Resource warning:', error);
}
});
console.log('Canvas produced; resource warnings:', failedResources);An old example uses onrendered
Older snippets may show an onrendered option. That callback was removed in favor of the Promise-returning API. Replace it with await html2canvas(...) or .then(...); adding the old option will not provide a current completion signal.
The output changes between runs
Freeze application state before capture. Pause carousels or animations, use a capture-only class, wait for a stable layout frame, and avoid starting multiple captures against the same changing element. If the page must be pixel-identical, control fonts, image dimensions, viewport size, and device scale in your own code.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Performance and reliability choices
- Capture only what you need. A smaller subtree uses less memory and finishes sooner than the entire document.
- Avoid duplicate renders. Debounce buttons and state-change handlers so one user action does not start several expensive Promise operations.
- Choose scale deliberately. Higher canvas scale improves detail but increases memory and encoding time.
- Keep ownership of readiness. html2canvas has no universal callback that means every application resource, font, animation, or asynchronous state is ready. Define those preconditions yourself.
- Handle rejection. Report a useful message, preserve the original error for logging, and offer a retry only when the underlying condition can change.
Finally, remember the product boundary: html2canvas is a DOM reconstruction library, not a browser-pixel recorder. Unsupported CSS, cross-origin content, and browser rendering differences can remain even when its Promise fulfills.
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Or skip the browser setup
If your goal is a server-side website screenshot rather than a canvas generated inside your page, ScreenshotNeo provides a GET-based screenshot API and an MCP server for AI clients such as Claude and Cursor. It accepts consent banners before capture and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each step can be disabled. Only clean shots are billed: bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and the response identifies the result with X-Page-Verdict and X-Billed headers.
One request with cURL
See the ScreenshotNeo documentation for parameter details.
curl -G "https://api.screenshotneo.com/v1/shot"
-d access_key=YOUR_API_KEY
--data-urlencode url=https://stripe.com
-o shot.webpPython
import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
r.raise_for_status()
open("shot.webp", "wb").write(r.content)Node.js
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
if (!res.ok) throw new Error(`Screenshot failed: ${res.status}`);
const buffer = Buffer.from(await res.arrayBuffer());
require('fs').writeFileSync('shot.webp', buffer);Options for production captures
ScreenshotNeo supports full-page captures with lazy images loaded, CSS-selector element capture, dark mode, 12 device presets or custom viewports, retina scale, PDF paper size/margins/orientation/page ranges, HTML/CSS input, custom JavaScript and CSS, pre-capture clicks, hidden selectors, waits for a selector, delay, or network idle, blocking ads, trackers, requests, or resource types, custom headers/cookies/user agents/Authorization, timezone and geolocation, transparent backgrounds, image resizing, caller-selected cache TTLs, signed links for public image tags, asynchronous jobs with signed webhooks, bulk capture of up to 100 URLs per call, a usage API, an OpenAPI specification, and familiar parameter names for easier migration.
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Quick Recap
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