Scusate ragazzi ma perchè l'evento touchstart non viene visto anche se mq.matches è true? 
codice:
<head>
<style>
.text {
color: #000;
font-size: 32px;
font-weight: 700;
opacity: 0;
text-align: center;
transition: opacity .4s ease;
}
.text.show {
opacity: 1;
}
@media screen and (max-width: 500px) {
.text {
color: steelblue;
}
}
</style>
</head>
<body>
<p class="text">Hello, World! : )</p>
<button>CLICK ME</button>
<script>
const text = document.querySelector('.text');
const btn = document.getElementsByTagName('button')[0];
const mq = window.matchMedia('(max-width: 500px)');
function showText(event) {
btn.addEventListener(event, () => {
console.log('event ', event);
text.classList.toggle('show');
});
}
mq.matches ? showText('touchstart') : showText('click');
</script>
</body>