Canvas toBlob vs toDataURL: Performance and Use Cases
When to use each Canvas export API and their performance implications for large images.
SJ
Sarah Jenkins
Contributing Author · Squoosh Next BlogCanvas.toDataURL returns a synchronous base64-encoded data URL string, while Canvas.toBlob provides an asynchronous callback with a Blob object. The performance difference is significant for large images. A 4000×3000px Canvas encoded as JPEG at quality 90 may produce a 3MB image.
As a data URL, this becomes a 4MB base64 string that must be allocated entirely in JavaScript memory as a string object. As a Blob, the same data exists in browser-managed binary memory outside the V8 heap, reducing GC pressure. For download links, create an object URL from the Blob with URL.createObjectURL — it resolves instantly and the browser streams the download from its memory cache.
Base64 data URLs in anchor href attributes force the browser to decode the base64 back to binary before downloading, wasting CPU time. Always use toBlob for exports and downloads, and reserve toDataURL only for cases that specifically require a string representation such as setting CSS background-image or injecting into an HTML attribute.
Key Takeaways
toDataURL returns a synchronous base64-encoded data URL string, while Canvas.
toBlob provides an asynchronous callback with a Blob object.
The performance difference is significant for large images.
A 4000×3000px Canvas encoded as JPEG at quality 90 may produce a 3MB image.
Try It in the Workspace
Everything discussed in this article can be tested directly in Squoosh Next — no sign-up, no upload, 100% client-side.