Effacer la fild
document.getElementById('inpu').value = ''
<input type="text" onfocus="this.value=''" value="Blabla">
Xanthous Xenomorph
document.getElementById('inpu').value = ''
<input type="text" onfocus="this.value=''" value="Blabla">
document.getElementById("msg").value = "";<h2 id="count-me">4</h2>
<button onclick="save()">Reset</button>
function save() {
// If what you want to reset is an integer
document.getElementById("count-me").textContent = 0;
// If what you want to reset is a textfield
document.getElementById("textfield1").value = "";
let count = 0; // If you create a count variable in Javascript
}