javascript encode - decode problems

Would anybody be so kind to tell me where the problem is? I want to encode and decode an simple input, but it does not work! Why? Thank you for your help ;)

ENCODE:

function codeschutz_encode(s, delta) {
    var temp = "";
    var alt, neu;
    for(var i = 0; i < s.length; i++) {
        alt = s.charCodeAt(i);
        if(alt >= 65 && alt <= 90) {
            neu = alt + delta;
            if(neu > 90) {
                neu -= 26;
            }
        } else if (alt >= 97 && alt <= 122) {
            neu = alt + delta;
            if (neu > 122) {
                neu -= 26;
            };
        } else {
            neu = alt;
        }
        temp += String.formCharCode(neu);
    }
    return temp;
}

DECODE:

function codeschutz_decode(s, delta) {
    var temp = "";
    var temp, neu;
    for (var i = 0; i < s.length; i++) {
        alt = s.CharCodeAt(i);
        if (alt >= 65 && alt <= 90) {
            neu = alt - delta;
            if (neu < 65) {
                neu += 26;
            }
        } else if (LT >= 97 && alt <= 122) {
            neu = alt - delta;
            if (neu < 97) {
                neu += 26;
            }
        } else {
            neu = alt;
        }
        temp += String.formCharCode(neu);
    }
    return temp;
}

HTML: I created a textarea for the input and a textare for the output

<html>
<head>
    <meta  charset="UTF-8">
    <title>verschlüsseln |</title>
    <link rel="stylesheet" type="text/css" href="encode.js">
    <link rel="stylesheet" type="text/css" href="decode.js">

    <script type="text/javascript">

        function encode(f) {
            var eingabe = f.elements["eingabe"].value;
            var delta = parseInt(f.elements["delta"].value);
            var ausgabe = codeschutz_encode(eingabe, delta);
            f.elements["ausgabe"].value = ausgabe;
        }

    </script>

</head>
<body>

    <form onsubmit="return false;">
        <textarea name="eingabe" cols ="70" rows="10"></textarea> <br />
        <input type="text" name="delta" value="13" />
        <input type="button" value="Kodieren" onclick="encode(this.form);" />
        <textarea name="ausgabe" cols="70" rows="10" onfocus="this.blur();"></textarea>

</body>
</html>

Solution

HTML

<html>
<head>
    <meta  charset="UTF-8">
    <title></title>
    <link rel="stylesheet" type="text/css" href="encode.js">
    <link rel="stylesheet" type="text/css" href="decode.js">

    <script type="text/javascript">

        function encode(f) {
            var eingabe = f.elements["eingabe"].value;
            var delta = parseInt(f.elements["delta"].value);
            var ausgabe = codeschutz_encode(eingabe, delta);
            f.elements["ausgabe"].value = ausgabe;
        }

    </script>

</head>
<body>

    <form onsubmit="return false;">
        <textarea name="eingabe" cols ="70" rows="10"></textarea> <br />
        <input type="text" name="delta" value="13" />
        <input type="button" value="Kodieren" onclick="encode(this.form);" />
        <textarea name="ausgabe" cols="70" rows="10" onfocus="this.blur();"></textarea>

</body>
</html>

DECODE:

function codeschutz_decode(s, delta) {
    var temp = "";
    var temp, neu;
    for (var i = 0; i < s.length; i++) {
        alt = s.CharCodeAt(i);
        if (alt >= 65 && alt <= 90) {
            neu = alt - delta;
            if (neu < 65) {
                neu += 26;
            }
        } else if (alt >= 97 && alt <= 122) {
            neu = alt - delta;
            if (neu < 97) {
                neu += 26;
            }
        } else {
            neu = alt;
        }
        temp += String.formCharCode(neu);
    }
    return temp;
}

ENCODE:

function codeschutz_encode(s, delta) {
    var temp = "";
    var alt, neu;
    for(var i = 0; i < s.length; i++) {
        alt = s.charCodeAt(i);
        if(alt >= 65 && alt <= 90) {
            neu = alt + delta;
            if(neu > 90) {
                neu -= 26;
            }
        } else if (alt >= 97 && alt <= 122) {
            neu = alt + delta;
            if (neu > 122) {
                neu -= 26;
            };
        } else {
            neu = alt;
        }
        temp += String.formCharCode(neu);
    }
    return temp;
}