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Issue WebAudio#220 - Rewrite the requestMIDIAccess algorithm (part 1)
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‎index.html

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@@ -193,8 +193,9 @@ <h2>
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</dt>
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<dd>
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<p>
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When invoked, returns a Promise object representing a request for
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access to MIDI devices on the user's system.
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When invoked the {{Navigator/requestMIDIAccess()}} method returns
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a promise that represents a request for access to MIDI devices on
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the user's system.
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</p>
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<p>
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Requesting MIDI access SHOULD prompt the user for access to MIDI
@@ -216,106 +217,170 @@ <h2>
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</p>
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<p data-link-for="Navigator">
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When the {{requestMIDIAccess()}} method is called, the user agent
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MUST run the <dfn>algorithm to request MIDI Access</dfn>:
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MUST run the following steps:
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</p>
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<ol>
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<li>
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<p>
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Let <var>promise</var> be a new Promise object and
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<var>resolver</var> be its associated resolver.
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</p>
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</li>
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<li>
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<p>
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Return <var>promise</var> and run the following steps
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asynchronously.
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</p>
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</li>
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<li>
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<p>
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Let <var>document</var> be the calling context's
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<a>Document</a>.
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</p>
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</li>
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<li>
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<p>
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If <var>document</var> is not <a>allowed to use</a> the
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<a>policy-controlled feature</a> named <a>midi</a>, jump to
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the step labeled <em>failure</em> below.
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</p>
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</li>
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<li>
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<p>
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Optionally, e.g. based on a previously-established user
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preference, for security reasons, or due to platform
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limitations, jump to the step labeled <em>failure</em> below.
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</p>
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</li>
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<li>
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<p>
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Optionally, e.g. based on a previously-established user
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preference, jump to the step labeled <em>success</em> below.
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</p>
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</li>
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<li>
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<p>
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Prompt the user in a user-agent-specific manner for
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permission to provide the entry script's origin with a
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{{MIDIAccess}} object representing control over user's MIDI
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devices. This prompt may be contingent upon whether system
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exclusive support was requested, and may allow the user to
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enable or disable that access.
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</p>
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<p>
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If permission is denied, jump to the step labeled
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<em>failure</em> below. If the user never responds, this
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algorithm will never progress beyond this step. If permission
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is granted, continue the following steps.
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</p>
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</li>
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<li>
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<p>
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<em><b>success</b></em>: Let <var>access</var> be a new
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{{MIDIAccess}} object. (It is possible to call
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requestMIDIAccess() multiple times; this may prompt the user
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multiple times, so it may not be best practice, and the same
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instance of MIDIAccess will not be returned each time.)
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</p>
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</li>
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<li>
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<p>
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Call <var>resolver</var>'s <code>accept(value)</code> method
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with <var>access</var> as value argument.
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</p>
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</li>
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<li>
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<p>
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Terminate these steps.
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</p>
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</li>
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<li>
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<p>
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<em><b>failure</b></em>: Let <var>error</var> be a new
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{{DOMException}}. This exception's .name should be
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{{"SecurityError"}} if the user or their security settings
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denied the application from creating a MIDIAccess instance
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with the requested options, or if the error is the result of
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<var>document</var> not being <a>allowed to use</a> the
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feature, {{"AbortError"}} if the page is going to be closed
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for a user navigation, {{"InvalidStateError"}} if the
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underlying systems raise any errors, or otherwise it should
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be {{"NotSupportedError"}}.
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Let <var>promise</var> be [=a new promise=].
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</p>
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</li>
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<li>
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<p>
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Call <var>resolver</var>'s <code>reject(value)</code> method
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with <var>error</var> as value argument.
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Run the following steps [=in parallel=]:
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</p>
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</li>
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<ol>
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<li>
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<p>
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Let <var>document</var> be the calling context's
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<a>Document</a>.
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</p>
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</li>
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<li>
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<p>
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If <var>document</var> is not <a>allowed to use</a> the
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<a>policy-controlled feature</a> named <a>"midi"</a>, then:
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<ol>
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<li>
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<p>
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[=Deny MIDI access=] with |promise| and
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{{"SecurityError"}}.
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</p>
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</li>
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<li>
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<p>Return |promise|.</p>
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</li>
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</ol>
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</p>
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</li>
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<li>
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<p>
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Optionally, e.g. based on a previously-established user
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preference, for security reasons, or due to platform
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limitations:
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<ol>
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<li>
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<p>
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Let |exception name| be {{"SecurityError"}} if the
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user or their security settings denied the application
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from creating a {{MIDIAccess}} instance with the
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requested options, {{"AbortError"}} if the
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page is going to be closed for a user navigation,
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{{"InvalidStateError"}} if the underlying systems
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raise any errors, or otherwise to
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{{"NotSupportedError"}}.
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</p>
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<li>
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<p>
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[=Deny MIDI access=] with |promise| and
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|exception name|.
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</p>
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</li>
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<li>
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<p>Return |promise|.</p>
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</li>
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</li>
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</ol>
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</p>
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</li>
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<li>
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<p>
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Optionally, e.g. based on a previously-established user
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preference:
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<ol>
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<li>
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<p>
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[=Grant MIDI access=] with |promise|.
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</p>
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</li>
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<li>
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<p>Return |promise|.</p>
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</li>
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</ol>
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</p>
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</li>
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<li>
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<p>
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Prompt the user in a user-agent-specific manner for
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permission to provide the entry script's origin with a
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{{MIDIAccess}} object representing control over user's MIDI
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devices. This prompt may be contingent upon whether system
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exclusive support was requested, and may allow the user to
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enable or disable that access:
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<ol>
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<li>
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<p>
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If permission is denied:
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<ol>
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<li>
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<p>
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[=Deny MIDI access=] with |promise| and
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{{"SecurityError"}}.
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</p>
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</li>
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<li>
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<p>Return |promise|.</p>
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</li>
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</ol>
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</p>
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</li>
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<li>
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<p>
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If permission is granted:
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</p>
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<ol>
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<li>
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<p>
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[=Grant MIDI access=] with |promise|.
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</p>
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</li>
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<li>
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<p>Return |promise|.</p>
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</li>
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</ol>
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</p>
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</li>
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</ol>
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</p>
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</li>
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</ol>
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</ol>
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</dd>
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</dl>
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<p>
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To <dfn>deny MIDI access</dfn> with |promise| and |exception name|,
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run these steps:
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<ol>
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<li>
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<p>Let |error| be a new {{DOMException}} with its
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{{DOMException/name}} set to |exception name|.</p>
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</li>
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<li>
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<p>[=Reject=] |promise| with |error|.</p>
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</li>
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</ol>
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</p>
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<p>
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To <dfn>grant MIDI access</dfn> with |promise|, run these
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steps:
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<ol>
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<li>
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<p>
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Let <var>access</var> be a new {{MIDIAccess}} object.
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</p>
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<p class="note">
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It is possible to call {{Navigator/requestMIDIAccess()}}
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multiple times; this may prompt the user multiple times, so it
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may not be best practice, and the same instance of
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{{MIDIAccess}} will not be returned each time.
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</p>
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</li>
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<li>
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<p>[=Resolve=] |promise| with |access|.</p>
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</li>
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</ol>
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</p>
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</section>
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<section data-dfn-for="MidiPermissionDescriptor" data-link-for="Navigator">
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<h2 id="MidiPermissionDescriptor">

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