This page will automatically play "hello" with jscwlib. Note that by default, most browsers will generally not allow autoplay any more, but require some sort of user interaction to play sounds (see MDN).
In Firefox, to ensure that autoplay works on a site, go to your preferences, and look for Block websites from automatically playing sound (checked by default), and click on "Exceptions". Then enter the URL of the site you like to allow autoplay for (e.g. "fkurz.net") and click on "Save".
The autoplay restrictions are valid for all audio sources, e.g. also for
<audio src="/music.mp4" autoplay>.