How to decode a Base64 string in JScript

Question

I have to decode a Base64 String in JScript, and I've tried this code for performing the purposed action :

var xmlDom = new ActiveXObject("Microsoft.XMLDOM");
var el = xmlDom.createElement("tmp");
el.dataType = "bin.Base64"
el.text = "aGVsbG8gd29ybGQ=";
WScript.Echo(el.nodeTypedValue);

But, unfortunately, It doesn't work. It should show the message Hello world but the return message is a bunch of Chinese characters. Here's a screen as proof

And, Is there another method for decoding a Base64 encoded string?

Martin · Accepted Answer · 2018-12-07 16:17:54Z

1

You have to carry out some additional steps to get the textual representation of the decoded base-64.

The result of el.nodeTypedValue will be an array of bytes containing the decoded base-64 data. This needs to be converted into a textual string. I have assumed utf-8 for the example but you may need to modify it to suit your text encoding.

var xmlDom = new ActiveXObject("Microsoft.XMLDOM");
var el = xmlDom.createElement("tmp");
el.dataType = "bin.Base64"
el.text = "aGVsbG8gd29ybGQ=";
//WScript.Echo(el.nodeTypedValue);

// Use a binary stream to write the bytes into
var strm = WScript.CreateObject("ADODB.Stream");
strm.Type = 1;
strm.Open();
strm.Write(el.nodeTypedValue);

// Revert to the start of the stream and convert output to utf-8
strm.Position = 0;
strm.Type = 2;
strm.CharSet = "utf-8";

// Output the textual equivalent of the decoded byte array
WScript.Echo(strm.ReadText());
strm.Close();

Here is the output:

Note that this code is not production-worthy. You'll need to tidy up objects after their use is complete.

There are other ways of converting an array of bytes to characters. This is just one example of it.

answered Dec 7, 2018 at 16:17

Martin

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1 Comment

Eugen-Andrei Coliban Over a year ago

Thanks, this one helped me :)

LesFerch · Accepted Answer · 2023-04-26 16:11:58Z

1

If you run the JScript code from an HTA, you can use atob:

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=11">
</head>
<body>
<script language="JScript">
  text = "Hello world!";
  encoded = window.btoa(text);
  alert(encoded);
  decoded = window.atob(encoded);
  alert(decoded);
  self.close();
</script>
</body>
</html>

answered Apr 26, 2023 at 16:11

LesFerch

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