[whatwg] Proposing <canvas>.toBlob(contentType)

Juriy Zaytsev kangax at gmail.com
Wed Apr 13 15:36:31 PDT 2011

I would be in favor of this.

In my recent app — http://mustachified.com — I used `mozGetAsFile` to
retrieve file from canvas, append it to form data and send to an external
service via cross-domain request.

When mozGetAsFile was not available, I had to build blob manually from
canvas' data url. Aside from the fact that it's more code to
transfer/maintain, and (likely) worse performance, the blob building also
relies on presence of BlobBuilder, ArrayBuffer and Uint8Array — so is not
always available.

Source: http://mustachified.com/master.js


On Wed, Apr 13, 2011 at 6:02 PM, Kyle Huey <me at kylehuey.com> wrote:

> Hello All,
> Gecko 2.0 ships with a non-standard method on <canvas> named
> mozGetAsFile(contentType, fileName).  We added this for internal use in our
> UI.  It retrieves the contents of the canvas as a File object (at the time
> Gecko did not supports Blobs) encoded in the contentType according to the
> same rules toDataURL uses.
> I propose adding a toBlob(contentType) method to the canvas element in the
> style of toDataURL.  This would greatly increase the options available to
> developers for extracting data from a canvas element (a Blob can be saved
> to
> disk, XHRed, etc.)
> - Kyle

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