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Editorial Team
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Asked: 2026-06-04T23:27:43+00:00

I have a simple code fragment which does Base64 decoding on the contents of

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I have a simple code fragment which does Base64 decoding on the contents of a textbox when a button is clicked on.

When loaded in IE9, it works exactly as expected, but in Firefox 12, clicking on the button doesn’t do anything.

The code is here:

<html>
<head>
    <script type="text/javascript">

  var keyStr = "ABCDEFGHIJKLMNOP" +
               "QRSTUVWXYZabcdef" +
               "ghijklmnopqrstuv" +
               "wxyz0123456789+/" +
               "=";

  function decode64(input) {
     var output = "";
     var chr1, chr2, chr3 = "";
     var enc1, enc2, enc3, enc4 = "";
     var i = 0;

     // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
     var base64test = /[^A-Za-z0-9\+\/\=]/g;
     if (base64test.exec(input)) {
        alert("There were invalid base64 characters in the input text.\n" +
              "Valid base64 characters are A-Z, a-z, 0-9, '+', '/',and '='\n" +
              "Expect errors in decoding.");
     }
     input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

     do {
        enc1 = keyStr.indexOf(input.charAt(i++));
        enc2 = keyStr.indexOf(input.charAt(i++));
        enc3 = keyStr.indexOf(input.charAt(i++));
        enc4 = keyStr.indexOf(input.charAt(i++));

        chr1 = (enc1 << 2) | (enc2 >> 4);
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
        chr3 = ((enc3 & 3) << 6) | enc4;

        output = output + String.fromCharCode(chr1);

        if (enc3 != 64) {
           output = output + String.fromCharCode(chr2);
        }
        if (enc4 != 64) {
           output = output + String.fromCharCode(chr3);
        }

        chr1 = chr2 = chr3 = "";
        enc1 = enc2 = enc3 = enc4 = "";

     } while (i < input.length);

     return unescape(output);
  }
String.prototype.trim = function() {
        return this.replace(/^\s+|\s+$/g,"");
}
function decodeHtml(){
        var contentdiv = document.getElementById("html");
        var targetdiv = document.getElementById("target");
        targetdiv.innerHTML = decode64(contentdiv.innerHTML.trim());
}
        </script>
</head>
        <body>
                <textarea id="html">
                </textarea>
                <button onClick="decodeHtml()">Decode</button><br><br>
                <div id="target"></div>
        </body>
</html>
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1 Answer

  1. Editorial Team

    Shouldn’t the last line:

    targetdiv.innerHTML = decode64(contentdiv.innerHTML.trim());

    be:

    targetdiv.innerHTML = decode64(contentdiv.value.trim());

    jsFiddle example.

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