fix: MidiBuffer should work without options.

[tomohirohiratsuka]

Acknowledgment

First of all, I would like to express my gratitude to the maintainers and contributors of abcjs for creating and maintaining such a powerful and versatile library. Your work has made it easier for developers like me to integrate musical notation and playback into web applications.

While exploring the synthesized sound functionality, I encountered a minor issue with the handling of the options parameter in MidiBuffer.init(). This PR is a small attempt to contribute back and improve the library further. Thank you for your continued efforts in maintaining this project and for considering this contribution.

Problem

In the current implementation of MidiBuffer.init(), the options.options parameter is set to undefined by default(reference). However, the code does not properly initialize this parameter, resulting in an error when MidiBuffer.prime() attempts to access self.options.swing. Specifically, at this line, the code tries to reference self.options.swing without handling the case where self.options is undefined.

This leads to the following error during playback:

TypeError: Cannot read properties of undefined (reading 'swing')

Proposed Solution

Modify the condition at create-synth.js#L318 to safely access self.options.swing by using optional chaining (self.options?.swing). This ensures that prime() does not throw an error if self.options is undefined.

This fix aligns with the existing behavior of MidiBuffer.init() and ensures that the function works seamlessly without requiring options to be explicitly defined.

Additional Context

If the current behavior is intentional and options is expected to be initialized as an empty object when not provided, an alternative approach would be to ensure options is always initialized within MidiBuffer.init().

Alternative Fix

self.options = options || {};

This would ensure that self.options is always defined, avoiding the need for optional chaining in subsequent references.