Untitled

<html>
<head>
    <meta charset="UTF-8">
</head>
<body>
    <form name="a">
        <input type="text" name="haslo" onkeyup="sila()">
    </form>
    <div id="czysilne"></div>
    <script>
        function sila()
        {
            var haslo = document.a.haslo.value;
            var sila;
            if(haslo.length>=7 && /[0-9]/.test(haslo))sila="Silne";
            else if(haslo.length>=4)sila="Średnie";
            else sila="Słabe";
            document.getElementById("czysilne").innerHTML=sila;
        }
    </script>
</body>
</html>