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html2canvas throws IndexSizeError when a zero or otherwise invalid width or height reaches the Canvas 2D drawImage() call. The usual causes are a hidden or collapsed capture target, a component captured before layout, an empty child canvas, or an image whose intrinsic dimensions are still zero. Verify dimensions immediately before capture, wait for layout and assets, make capture-only changes in onclone, and instrument resource failures. The workflow below fixes the error without changing the live page.
What the error means
IndexSizeError is the browser’s Canvas 2D argument-validation error. In html2canvas, the renderer eventually calls drawImage() with dimensions calculated from your DOM and its images or canvases. A width or height of zero (or another invalid numeric value) can make that call fail. The same symptom is often reported as “Failed to execute drawImage on CanvasRenderingContext2D” or “image argument is a canvas element with a width or height of 0.”
html2canvas may allocate an intermediate canvas with at least one pixel, but that does not guarantee that the later draw operation receives positive requested dimensions. Therefore, changing only the output canvas size does not repair the underlying invalid element or asset.
1. Check the capture target before calling html2canvas
Start by proving that the node exists, is attached, and has a positive rendered and scroll size. Run this immediately before the capture, not during an earlier mount phase.
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const node = document.querySelector('#capture');
if (!node) throw new Error('capture target missing');
const rect = node.getBoundingClientRect();
console.table({
rectWidth: rect.width,
rectHeight: rect.height,
scrollWidth: node.scrollWidth,
scrollHeight: node.scrollHeight,
display: getComputedStyle(node).display,
visibility: getComputedStyle(node).visibility
});
if (rect.width <= 0 || rect.height <= 0) {
throw new Error(`capture target has invalid size: ${rect.width}x${rect.height}`);
}A positive scrollWidth alone is not sufficient: an element can contain content while its rendered rectangle is zero because it or an ancestor is display:none, collapsed, detached, or otherwise not laid out.
Common dimension failures
- Hidden ancestor: a modal, tab, accordion panel, or route is still
display:none. - Not mounted or measured: a framework component has rendered its shell but has not completed its size calculation.
- Collapsed layout: flex/grid constraints, zero-height parents, or an off-screen technique that also removes layout.
- Empty child canvas: a chart or drawing surface was created with
width="0"orheight="0". - Unready media: an image, SVG, background, or nested canvas has no intrinsic dimensions at capture time.
2. Make hidden content renderable
Do not capture an element while it or a required ancestor is display:none. Render it visibly, place it off-screen while preserving layout, or alter only the cloned document used by html2canvas.
For a normal page, a capture-only class can preserve dimensions without showing the content to users:
.capture-staging {
position: absolute !important;
left: -100000px !important;
top: 0 !important;
display: block !important;
visibility: visible !important;
}
Apply the class after the component has mounted and remove it after capture. Avoid display:none, content-visibility:hidden, or a detached document for the target. If a parent controls visibility, fix the parent or use onclone so the live interface is untouched.
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3. Wait for layout, fonts, and images
Capture only after the browser has performed layout and the component has finished measuring itself. In a client-rendered application, that may mean waiting for the next animation frame after state changes. Wait for fonts as well, because a late font swap can change widths and heights.
await document.fonts?.ready;
await new Promise(requestAnimationFrame);
await new Promise(requestAnimationFrame);For images inside the target, resolve both already-complete images and images that are still loading. Treat an error as a completed wait so one broken URL does not leave your promise pending forever.
const images = [...node.querySelectorAll('img')];
await Promise.all(images.map(img => {
if (img.complete) return Promise.resolve();
return new Promise(resolve => {
img.addEventListener('load', resolve, { once: true });
img.addEventListener('error', resolve, { once: true });
});
}));
await Promise.all(images.map(img =>
typeof img.decode === 'function' ? img.decode().catch(() => {}) : Promise.resolve()
));Inspect every descendant canvas too:
for (const canvas of node.querySelectorAll('canvas')) {
if (canvas.width <= 0 || canvas.height <= 0) {
throw new Error(`invalid child canvas: ${canvas.width}x${canvas.height}`);
}
}4. Use onclone for safe capture-only fixes
html2canvas’s documented onclone option receives the cloned document. It is the right place to reveal sections marked for capture, remove animations, and give empty placeholders safe dimensions without mutating the user’s live page.
const canvas = await html2canvas(node, {
onclone: clonedDoc => {
clonedDoc.querySelectorAll('[data-capture-hidden]').forEach(el => {
el.removeAttribute('hidden');
el.style.display = 'block';
el.style.visibility = 'visible';
});
clonedDoc.querySelectorAll('*').forEach(el => {
el.style.setProperty('transition', 'none', 'important');
el.style.setProperty('animation', 'none', 'important');
});
}
});Only assign fallback dimensions when an empty placeholder is intentionally part of the design. Giving an accidentally broken chart a width does not recreate its data; fix the chart’s initialization first.
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5. Capture large or full-page content correctly
Blank or cut-off output can be a separate canvas-area problem. Set windowWidth and windowHeight to the target’s scroll dimensions when capturing a long element, and reduce scale if the resulting bitmap is too large.
const canvas = await html2canvas(node, {
windowWidth: Math.max(node.scrollWidth, 1),
windowHeight: Math.max(node.scrollHeight, 1),
scale: Math.min(window.devicePixelRatio || 1, 2),
backgroundColor: '#ffffff'
});If the page remains too large, capture smaller sections and stitch them, crop to the required region, or use a lower scale. Browser limits vary; Safari has stricter area behavior in the documented issue discussion, so test large captures in every browser you support. The often-repeated Safari area number of 5,242,880 pixels is user-reported in that discussion, not a universal browser specification.
6. Distinguish CORS failures from dimension failures
Remote images introduce a different class of problem. useCORS:true works only when the image server supplies an appropriate Access-Control-Allow-Origin response. Otherwise, use a same-origin proxy or change the asset delivery configuration.
const canvas = await html2canvas(node, {
useCORS: true,
allowTaint: false
});CORS errors typically taint the canvas or cause images to be skipped. They do not normally explain a zero-size drawImage() argument. Fix dimensions first, then investigate cross-origin headers if images are missing or the browser reports a security exception.
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7. Instrument the failing resource
Use the documented onError callback and the browser stack to identify whether the invalid dimensions came from an image, child canvas, background, SVG, or iframe.
const canvas = await html2canvas(node, {
onError: error => {
console.error('html2canvas resource failed', error);
}
});When the stack points into an image or canvas draw, temporarily remove half of the target’s children, capture again, and narrow the failing subtree. Log each candidate’s naturalWidth/naturalHeight for images and width/height for canvases. This binary-search approach is faster than changing random html2canvas options.
A defensive end-to-end example
async function captureElement(selector) {
const node = document.querySelector(selector);
if (!node) throw new Error('capture target missing');
const rect = node.getBoundingClientRect();
if (rect.width <= 0 || rect.height <= 0) {
throw new Error(`capture target has invalid size: ${rect.width}x${rect.height}`);
}
await document.fonts?.ready;
await Promise.all([...node.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 });
});
}));
for (const child of node.querySelectorAll('canvas')) {
if (child.width <= 0 || child.height <= 0) {
throw new Error(`invalid child canvas: ${child.width}x${child.height}`);
}
}
return html2canvas(node, {
windowWidth: Math.max(node.scrollWidth, 1),
windowHeight: Math.max(node.scrollHeight, 1),
scale: Math.min(window.devicePixelRatio || 1, 2),
useCORS: true,
onclone: clonedDoc => {
clonedDoc.querySelectorAll('[data-capture-hidden]').forEach(el => {
el.removeAttribute('hidden');
el.style.display = 'block';
});
},
onError: error => console.error('html2canvas resource failed', error)
});
}Troubleshooting by symptom
| Symptom | Likely cause | Fix |
|---|---|---|
IndexSizeError immediately |
Target or child canvas has a zero dimension | Log rectangles and canvas sizes; render hidden ancestors and initialize canvases before capture. |
| Fails only on a tab or modal | Panel is display:none until opened |
Capture while open, stage it off-screen, or reveal it in onclone. |
| Fails intermittently | Race with layout, fonts, or image decoding | Wait for mount, two animation frames, document.fonts.ready, and image completion. |
| Images missing, security exception | Cross-origin response lacks CORS headers | Enable server CORS or proxy images through your origin; keep useCORS:true. |
| Blank or cut-off long image | Canvas area or viewport dimensions are too large | Match window dimensions, lower scale, crop, or tile; test Safari separately. |
| Only one widget breaks the capture | Invalid SVG, iframe, background, image, or nested canvas | Use onError, inspect the stack, and isolate descendants until the resource is found. |
When to use a different capture method
html2canvas reconstructs a page from the DOM and CSS, so it can diverge from browser pixels and cannot freely read cross-origin content. Compare approaches on DOM fidelity, browser-native fidelity, cross-origin asset support, maximum capture area, whether the code runs in an ordinary page or an extension, and maintenance cost. The html2canvas FAQ notes that major browsers expose native screenshot APIs in extension APIs that are more reliable and do not have canvas size limits. Those APIs require an extension context; they are not a drop-in replacement for a script running on an ordinary website.
Or skip the browser setup
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FAQ
Does setting scale: 1 fix IndexSizeError?
It can reduce oversized-canvas failures, but it does not make a hidden target, empty canvas, or zero-dimension image valid. Check dimensions first.
Can I capture an iframe with html2canvas?
Only same-origin iframe content can be inspected as ordinary DOM. Cross-origin frames remain isolated by the browser’s security model.
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A retry without changing layout or asset state usually repeats the same invalid draw. Retry only after the failing dimension or readiness condition has been corrected.
Frequently Asked Questions
Does setting scale: 1 fix IndexSizeError?
It can reduce oversized-canvas failures, but it does not make a hidden target, empty canvas, or zero-dimension image valid. Check dimensions first.
Can I capture an iframe with html2canvas?
Only same-origin iframe content can be inspected as ordinary DOM. Cross-origin frames remain isolated by the browser’s security model.
Should I catch the exception and retry?
A retry without changing layout or asset state usually repeats the same invalid draw. Retry only after the failing dimension or readiness condition has been corrected.
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