JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" id="eleve" value="eleve" />
<label for="eleve">eleve</label>
<br />
<input type="checkbox" id="prof" value="prof" />
<label for="prof">prof</label>
<br />
<input type="checkbox" id="admin" value="admin" />
<label for="admin">admin</label>
<br />
<input type="button" id="bar" value="verif" />

JavaScript

var MonTableau = new Array();

function validate() {

    if (document.getElementById('eleve').checked) {
               MonTableau[0] = "eleve";
    }

    if (document.getElementById('prof').checked) {
        MonTableau[1] = "prof";
    }

    if (document.getElementById('admin').checked) {
        MonTableau[2] = "admin";
    }

} //validate


function ReturnTab () {
    alert(MonTableau);

} //ReturnTab

$(':checkbox').change(validate);
$('#bar').click(ReturnTab);