JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="champdunom" id="un" onBlur="envoyer(1)"/>
  <input type="submit" name="submit"/>
<script>
    function envoyer(num){
        var valeurchamp = document.getElementById('un').value; 
        alert('Test');   
    }
</script>