JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="textcopy1" class="textcopy1" value="azerty">
<button class="copy" id="copy" rel="1">Copier</button>
<input type="text" id="textcopy2" class="textcopy2" value="ytreza">
<button class="copy" id="copy" rel="2">Copier</button>

JavaScript

function copy(element){
    var copyDiv = document.getElementById('textcopy'+element);
    //var copyDiv = document.getElementsByClassName('textcopy'+element);
    //alert('textcopy'+element);
    copyDiv.focus();
    document.execCommand('SelectAll');
    document.execCommand("Copy", false, null);
}
document.addEventListener("DOMContentLoaded", function () {
	//document.getElementsByClassName('copy');
	document.getElementById('copy').onclick = function() {
        //alert(this.getAttribute("rel"));
    	copy(this.getAttribute("rel"));
	}
});