html2canvas does not accept an HTML string directly. It accepts a DOM element. Put the string in a temporary, document-attached element, wait for fonts and images, then call await html2canvas(element, options). The Promise resolves to an HTMLCanvasElement that you can display, convert to a data URL, or export as a Blob.
The working pattern
Install or import html2canvas in your browser application, create a host element, assign the string to it, attach the host to document.body, and capture it. Attaching matters: a detached node has no normal document layout context, so computed styles, media queries, and resource resolution can be wrong or missing.
import html2canvas from '@html2canvas/html2canvas';
export async function renderHtmlString(html, options = {}) {
const host = document.createElement('div');
host.innerHTML = html;
host.style.position = 'fixed';
host.style.left = '-100000px';
host.style.top = '0';
host.style.width = 'fit-content';
document.body.appendChild(host);
try {
return await html2canvas(host, {
backgroundColor: null,
...options
});
} finally {
host.remove();
}
}
Use the function from a click handler, component action, or other browser-side code:
const html = `
<article class="card">
<h1>Invoice #1042</h1>
<p>Total: <strong>$149.00</strong></p>
</article>
`;
const canvas = await renderHtmlString(html, {
backgroundColor: '#ffffff',
scale: 2
});
document.querySelector('#preview').replaceChildren(canvas);
The library runs entirely in the browser; it is not a Node.js HTML renderer. The returned canvas is the result, not an image file by itself.
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Turn the canvas into an image or upload
Data URL
const pngDataUrl = canvas.toDataURL('image/png');
const img = new Image();
img.src = pngDataUrl;
document.body.appendChild(img);
A data URL is convenient for a preview, but large captures consume memory. For downloads or uploads, a Blob is usually better.
Blob download
canvas.toBlob((blob) => {
if (!blob) throw new Error('Canvas export failed');
const link = document.createElement('a');
link.href = URL.createObjectURL(blob);
link.download = 'capture.png';
link.click();
URL.revokeObjectURL(link.href);
}, 'image/png');
For JPEG, pass 'image/jpeg' and a quality value between 0 and 1. PNG preserves transparency and is the safer default for text and UI screenshots.
Safely handling the HTML string
innerHTML treats the string as markup. If any part comes from a user, database, URL, or other untrusted source, sanitize it before insertion with a maintained HTML sanitizer. html2canvas paints content; it is not an HTML sanitizer and should not be used as a security boundary.
For a complete document string containing <html>, <head>, or <body>, parse with DOMParser, then copy the intended body content into the temporary host. A fragment is simpler when you control the template:
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const parsed = new DOMParser().parseFromString(html, 'text/html');
const host = document.createElement('div');
host.append(...parsed.body.childNodes);
document.body.appendChild(host);
Do not assume styles from the parsed document’s detached <head> will automatically apply. Load the stylesheet in the live page or copy the required styles into the live document.
Make fonts, images, and layout ready before capture
Fonts
Web fonts can still be loading when the capture starts. Wait for the browser’s font set:
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await document.fonts.ready;
const canvas = await renderHtmlString(html, options);
If a font fails to load, the browser may substitute another face. Verify the font request and compare output in the browser you will use for capture.
Images and cross-origin rules
Remote images must be reachable and permitted by browser security policy. Set useCORS: true only when the image server returns an appropriate Access-Control-Allow-Origin header:
const canvas = await renderHtmlString(html, {
useCORS: true
});
If you cannot change the image server, use a same-origin proxy that retrieves the image and serves it from your origin. The browser’s policy cannot be bypassed by html2canvas. allowTaint defaults to false; enabling it does not grant cross-origin access and can leave the canvas unreadable for export.
Wait for image elements when the string includes images:
const host = document.createElement('div');
host.innerHTML = html;
document.body.appendChild(host);
await Promise.all([...host.querySelectorAll('img')].map((img) => {
if (img.complete) return Promise.resolve();
return new Promise((resolve) => {
img.addEventListener('load', resolve, { once: true });
img.addEventListener('error', resolve, { once: true });
});
}));
Integrate that wait into your temporary-host helper if image timing is important. An error event prevents a broken image from blocking forever, while still leaving you to decide whether a missing image should fail the operation.
Options that control the result
| Option | Use | Important behavior |
|---|---|---|
backgroundColor |
Set the canvas background | null preserves transparency. When no DOM background is present, the documented default is white. |
scale |
Control pixel density | Defaults to the device pixel ratio. Higher values sharpen output but increase memory and processing time. |
width, height |
Set capture dimensions | Use them to constrain the rendered area. |
x, y |
Crop the capture | Offsets define where capture begins within the element. |
windowWidth, windowHeight |
Control layout viewport values | Useful when media queries or long-page layout depend on viewport dimensions. |
useCORS |
Attempt CORS image loading | Works only when the server supplies the required CORS header. |
proxy |
Retrieve remote resources through a proxy | The proxy must be available to your application and return usable responses. |
foreignObjectRendering |
Ask the browser to render through SVG foreignObject where supported | It can help with some markup, but does not guarantee complete CSS fidelity. |
ignoreElements |
Exclude nodes programmatically | Provide a predicate that returns true for nodes to omit. |
data-html2canvas-ignore |
Exclude marked nodes | Add the attribute to an element you do not want painted. |
For example, this excludes a close button, preserves transparency, and captures at two-times density:
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const canvas = await renderHtmlString(html, {
backgroundColor: null,
scale: 2,
ignoreElements: (element) => element.matches('.close-button')
});
Long pages, cropping, and browser limits
A blank or partially captured result can mean that the requested bitmap exceeds the browser’s canvas-size limits. Large dimensions also multiply memory use: increasing both page size and scale can become expensive quickly.
For long content, measure the relevant scroll dimensions and provide viewport values that match the layout:
const canvas = await renderHtmlString(html, {
windowWidth: host.scrollWidth,
windowHeight: host.scrollHeight,
width: host.scrollWidth,
height: host.scrollHeight
});
If the page is still too large, capture sections separately and combine the resulting images, or reduce scale. Use x, y, width, and height for deliberate crops instead of relying on accidental viewport clipping.
Why CSS does not always match the browser
html2canvas reconstructs the picture rather than asking the browser for a native screenshot. Its project documentation notes that every CSS property must be implemented manually, so full CSS support is not promised. Advanced effects, unusual filters, complex blending, and browser-specific rendering can differ.
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- Use
foreignObjectRenderingas an experiment where your target browser supports it, not as a fidelity guarantee. - Wait for fonts and images before comparing output.
- Test in the same browser engine and viewport used in production.
This distinction also explains why an html2canvas image is not necessarily identical to a screenshot made by browser automation.
Common failures and fixes
Nothing renders from the string
Cause: the host is detached or has no measurable layout. Fix: append it to a live document before calling html2canvas, and inspect its dimensions before capture.
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The canvas is blank or cut off
Cause: incorrect viewport or element dimensions, or a browser canvas-size limit. Fix: set appropriate windowWidth/windowHeight, inspect scrollWidth and scrollHeight, reduce scale, or capture in sections.
Images are missing
Cause: the image has not loaded, the URL failed, or the origin does not permit CORS. Fix: wait for image load, verify the URL, set useCORS: true only with a matching server header, or use a same-origin proxy.
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Cause: a cross-origin resource was painted without successful CORS authorization. Fix: serve the asset with the correct CORS header or proxy it; changing allowTaint does not defeat browser security.
Fonts or advanced CSS look different
Cause: fonts were not ready or a CSS feature is not implemented by html2canvas. Fix: await document.fonts.ready, simplify the template, and test in the target browser.
The temporary content affects the visible page
Cause: the host participates in layout or has visible styling. Fix: position it off-screen as in the helper, give it an intentional width, and always remove it in a finally block.
Performance and reliability practices
- Keep the capture subtree small; omit navigation, animations, and controls that are not part of the image.
- Pause animations or use deterministic styles so repeated captures do not differ.
- Choose the lowest
scalethat meets your output requirement. - Wait for network-dependent assets explicitly instead of relying on timing guesses.
- Handle rejected Promises and export failures, and remove the temporary host even when capture fails.
- Remember that this is browser-side work: the user’s device, browser limits, and security policy affect the result.
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When to choose html2canvas
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Does html2canvas accept a complete HTML document string?
Not as its first argument. Parse the document, move the intended content into an element attached to the live page, and pass that DOM element to html2canvas.
Can html2canvas run in Node.js?
The library runs in the browser and depends on a live Window and document. Use a browser-capable renderer for Node-based automation instead.
Why is my output different from a native screenshot?
html2canvas reimplements CSS painting, so unsupported properties, fonts, browser differences, and cross-origin resources can change the result.
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