The requestMIDIAccess() method of the Navigator interface returns a Promise representing a request for access to MIDI devices on a user's system. This method is part of the Web MIDI API, which provides a means for accessing, enumerating, and manipulating MIDI devices.

This method may prompt the user for access to MIDI devices available to their system, or it may use a previously established preference to grant or deny access. If permission is granted then the Promise resolves and a MIDIAccess object is returned.

MIDIOptions Optional

An Object representing options to pass into the method. These options are:

sysex

A Boolean value that, if set to true, allows the ability to send and receive system exclusive (sysex) messages. The default value is false.

software

A Boolean value that, if set to true, allows the system to utilize any installed software synthesizers. The default value is false.

A Promise that resolves with a MIDIAccess object.

AbortError DOMException

Thrown if the document or page is closed due to user navigation.

InvalidStateError DOMException

Thrown if the underlying system raises any errors.

NotSupportedError DOMException

Thrown if the feature or options are not supported by the system.

SecurityError DOMException

Thrown if the user or system denies the application from creating a MIDIAccess object with the requested options, or if the document is not allowed to use the feature (for example, because of a Permission Policy, or because the user previously denied a permission request).

Access to the API is subject to the following constraints:

• The method must be called in a secure context.
• Access may be gated by the midi HTTP Permission Policy.
• The user must explicitly grant permission to use the API though a user-agent specific mechanism, or have previously granted permission. Note that if access is denied by a permission policy it cannot be granted by a user permission.

The permission status can be queried using the Permissions API method navigator.permissions.query(), passing a permission descriptor with the midi permission and (optional) sysex property:

navigator.permissions.query({ name: "midi", sysex: true }).then((result) => {
  if (result.state === "granted") {
    // Access granted.
  } else if (result.state === "prompt") {
    // Using API will prompt for permission
  }
  // Permission was denied by user prompt or permission policy
});

In the following example, the Navigator.requestMIDIAccess() method returns the MIDIAccess object, which gives access to information about the input and output MIDI ports.

navigator.requestMIDIAccess().then((access) => {
  // Get lists of available MIDI controllers
  const inputs = access.inputs.values();
  const outputs = access.outputs.values();
  // …
});

• Web MIDI API
• Introduction to Web MIDI