New Web IDL constructor syntax

[Boris Zbarsky]

As of today, the syntax for Web IDL constructors no longer involves an
extended attribute on the interface. There's now something that looks
more like a method named "constructor" with no explicitly-defined return
type.

So this:

[Constructor(DOMString str)]
interface MyInterface {};

is now written like so:

interface MyInterface {
constructor(DOMString str);
};

This means we can now specify extended attributes on the constructor,
and therefore we no longer assume that all constructors throw. If yours
does, you can use [Throws] in the usual way to indicate that:

interface ThrowingConstructor {
[Throws] constructor();
};

It may take some time for specifications to update to the new syntax
because not all of the tooling is updated yet; see
https://github.com/heycam/webidl/issues/778 which tracks that. So in
the meantime, including new spec IDL that uses constructors may require
some hand-editing to get it into the new form.

-Boris

[Christopher Mills]

Thanks Boris.

I've updated the MDN WebIDL guide to include a section on the new syntax:

https://developer.mozilla.org/en-US/docs/MDN/Contribute/Howto/Write_an_API_reference/Information_contained_in_a_WebIDL_file#New_constructor_syntax

(and the new Chrome-only syntax you talked about in your other mail:
https://developer.mozilla.org/en-US/docs/MDN/Contribute/Howto/Write_an_API_reference/Information_contained_in_a_WebIDL_file#Available_only_in_system_code
)

Chris Mills
MDN content lead & writers' team manager
Mozilla Developer Network <https://developer.mozilla.org/en-US/>
@chrisdavidmills <https://twitter.com/chrisdavidmills>

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[Boris Zbarsky]

On 9/13/19 3:54 AM, Christopher Mills wrote:
> I've updated the MDN WebIDL guide to include a section on the new syntax:

Chris,

Thank you!

-Boris