const elements = this.state.clients.map(function (client) {

    return (
      <li>
        {client.nom} <button>X</button>
      </li>
    );
  });
  

const elements = this.state.clients.map(function (client) ⇒ ( <li>

        {client.nom} <button>X</button>
      </li>
    );