XF 2.2 How to auto-assign a random unique ID value for each of the same type of custom BB code?

[ShikiSuen]

I am thinking of making a custom BB code relying on either VexFlow or ABCJS:
0xfe/vexflow: A JavaScript library for rendering music notation and guitar tablature. (github.com)
paulrosen/abcjs: javascript for rendering abc music notation (github.com)

However, both are rendering musical contents within a JavaScript and render to an HTML element with specified element ID (not HTML element class)...
... hence this question.