[FUNC] JSCRIPT urldecode

function URLDecode(encoded )
{
var HEXCHARS = "0123456789ABCDEFabcdef";
var plaintext = "";
var i = 0;
while (i < encoded.length)
{
var ch = encoded.charAt(i);
if (ch == "+")
{
plaintext += " ";
i++;
}
else if (ch == "%")
{
if (i < (encoded.length-2)
&& HEXCHARS.indexOf(encoded.charAt(i+1)) != -1
&& HEXCHARS.indexOf(encoded.charAt(i+2)) != -1 )
{
plaintext += unescape( encoded.substr(i,3) );
i += 3;
}
else
{
alert( 'error' + encoded.substr(i) );
plaintext += "%[ERROR]";
i++;
}
}
else
{
plaintext += ch;
i++;
}
}
return plaintext;
}