Legacy callback interface object.bs

<h4 id="legacy-callback-interface-object">Legacy callback interface object</h4>

The [=legacy callback interface object=] for a given [=callback interface=]
is a [=function object=].
It has properties that correspond to the [=constants=] defined on that interface,
as described in sections [[#es-constants]].

Note: Since an interface object is a [=function object=]
the <code>typeof</code> operator will return "function"
when applied to a [=legacy callback interface object=].

<div algorithm="create a legacy callback interface object">

    The [=legacy callback interface object=]
    for a given [=callback interface=] with [=identifier=] |id|
    and [=Realm=] |realm| is created as follows:

    1.  Let |steps| be the following steps:
        1.  [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
    1.  Let |F| be [=!=] [=CreateBuiltinFunction=](|realm|, |steps|, the [=%FunctionPrototype%=] of |realm|).
    1.  Perform [=!=] [=SetFunctionName=](|F|, |id|).
    1.  Perform [=!=] [=DefinePropertyOrThrow=](|F|, "length",
        PropertyDescriptor{\[[Value]]: 0, \[[Writable]]: <emu-val>false</emu-val>, \[[Enumerable]]: <emu-val>false</emu-val>, \[[Configurable]]: <emu-val>true</emu-val>}).
</div>

<h5 id="es-legacy-callback-interface-object-hasinstance">\[[HasInstance]]</h5>

<div algorithm="to invoke the internal [[HasInstance]] method of interface objects">

    The internal \[[HasInstance]] method of the [=legacy callback interface object=] |A|
    must behave as follows:

    1.  [=ECMAScript/throw=] a <emu-val>TypeError</emu-val> exception.
</div>