Add HTMLImageElement.isTypeSupported() #10055
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Give web developers a means to determine which formats are supported by the img element. Fixes #6324.
annevk
added
needs implementer interest
| <p>This specification does not specify which image types are to be supported.</p> | ||
| <p>A user agent has an associated <dfn>supported image MIME types</dfn> (a <span>set</span> of | ||
| <span data-x="MIME type">MIME types</span>). A user agent's <span>supported image MIME | ||
| types</span> is <span>implementation-defined</span>.</p> |
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It's worth double-checking there aren't places in "update the image data" that would benefit from direct references to this concept. E.g. maybe step 2? Or maybe the indirect reference in step 27 should be more direct? Not sure though.
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| of a multipage resource (e.g. a PDF file). User agents must not allow the resource to act in an | |||
| interactive fashion, but should honour any animation in the resource.</p> | |||
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| <p>This specification does not specify which image types are to be supported.</p> | |||
| <p>A user agent has an associated <dfn>supported image MIME types</dfn> (a <span>set</span> of | |||
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Can/should we be less implementation-defined for the case of a user agent with images disabled? Chrome still lets you toggle images for a site pretty easily using the site settings button accessed from the URL bar.
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I think that would be good, but do we have a processing model for images being disabled? https://html.spec.whatwg.org/#when-to-obtain-images suggests that images are either obtained immediately or on demand, but doesn't allow for them to be completely disabled. The specification model at least suggests to me that the supported image MIME type situation wouldn't change.
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https://html.spec.whatwg.org/#update-the-image-data step 2 seems like a reasonable processing model for images disabled. Not sure how battle-tested it is.
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| <li><p>If <var>mimeTypeRecord</var> is in the user agent's <span>supported image MIME | ||
| types</span> (and the user agent thus recognizes the <span data-x="MIME type | ||
| essence">essence</span> and all parameters (if any)), set <var>supported</var> to |
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Not sure exactly how parameter matching is supposed to work. Let's say a UA supports image/foo with the bar parameter set to any value. The MIME type record you get from parsing image/foo;bar=baz is not literally going to be in the set. (Unless the set is infinite in size; I guess in theory that's allowed.)
It feels like the "supported image MIME types" structure needs to get more complicated, to handle this sort of case?
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Fair, how about a map of MIME type essences to lists of parameter names?
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Well, that would solve my example, but what about if the UA supports image/foo;bar=X but only X? :)
I think it might be best to just have a UA-defined "supports image MIME type mimeType" predicate, which takes a MIME type and returns a boolean.
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That's fair. I guess we do want some words to make it so that unknown parameters or parameter values result in non-support.
| @@ -29217,9 +29219,17 @@ interface <dfn interface>HTMLImageElement</dfn> : <span>HTMLElement</span> { | |||
| </div> | |||
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| <dl class="domintro"> | |||
| <dt><code data-x=""><var>supported</var> = await <span>HTMLImageElement</span>.<span subdfn data-x="dom-img-isTypeSupported">isTypeSupported</span>(<var>mimeType</var>)</code></dt> | |||
| <dd> | |||
| <p>Returns a promise resolved with true, if <var>mimeType</var> is supported for the | |||
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Would it be worth linking "supported" to "supported image MIME types" here, just as helpful link for devs?
Give web developers a means to determine which formats are supported by the img element.
Fixes #6324.
(See WHATWG Working Mode: Changes for more details.)
/acknowledgements.html ( diff )
/embedded-content.html ( diff )
/images.html ( diff )