JSFiddle - React, Tailwind, and code Playground

HTML

<audio id="myAudio">
    <source src="http://www.sousound.com/music/healing/healing_01.mp3" preload="auto">
</audio>
<button id="playBtn" type="button" onclick="aud_play()">Play</button>
<button id="fadeBtn" type="button" onclick="aud_fade()">Fade</button>

JavaScript

var aud_play = function() {
    var myAudio = document.getElementById("myAudio");
    myAudio.volume = 1;
    myAudio.play();
};

var aud_fade = function() {
    var timer,
        myAudio = document.getElementById("myAudio");
    if (myAudio.volume > 0) {
        myAudio.volume -= 0.005;
        timer = setTimeout(aud_fade,5);
    }
};

var playBtn = document.getElementById('playBtn');
var fadeBtn = document.getElementById('fadeBtn');

playBtn.addEventListener('click', aud_play, false);
fadeBtn.addEventListener('click', aud_fade, false);