Untitled

<html>
<head>
    <meta charset="UTF-8">
</head>
<body>
    <div id="napis">Lubie placki</div>
    <form name="formularz">
        <input type="button" value="kliknij" onclick="f()">
    </form>
    <script>
        var x = 0;
        function f()
        {
            if(x==0)document.getElementById("napis").innerHTML = "";
            else if(x==1)document.getElementById("napis").innerHTML = "Lubie placki";
            x++;
            if(x>1)x=0;
        }
    </script>
</body>
</html>