Give <canvas>'s toDataURL() and toBlob() default parameter values

[annevk]

In IDL we can change type and quality to default to "image/png" and 1.0 respectively. E.g.,

USVString toDataURL(optional DOMString type = "image/png", optional any quality = 1.0);

This would then allow a slight simplification of their algorithms as the arguments are now always given. "a serialization of the bitmap as a file" can similarly take advantage as all callers will always provide these arguments now (and we no longer leave the default implementation-defined, as is already the case for OffscreenCanvas).

[donovanglover]

I changed the IDL, but I'm not sure which parts of the spec need to be updated. Can you give me some hints?

[annevk]

E.g., in step 3 of #dom-canvas-todataurl it says "if they were given", but now we've supplied defaults they will always be given so that can be stricken. The same goes for the a serialization of the bitmap as a file "algorithm" (more like a block of text in its current form). The arguments will always be passed so don't need to be marked optional and there's no need to talk about a default value there either (in the final paragraph before the note). Does that help?

[donovanglover]

Thanks, that helped a lot!

Edit: I assume that I do the same for toBlob() as well?

[TimothyGu]

@gloverdonovan Yup! We could replace "with type and quality if they were given" with "with type and quality" after the IDL change.