allowed chars in Javascript

Greetings

I am trying to limit characters that can be typed in the textbox on an asp.net web page. Only numbers 0-9 and the two alphabets S and T are allowed. small letter s and t can be allowed but changed to uppercase on keypress. Below is what I tried but it doesn't work.

Please assist!

MandyProg
Allowed-keys.txt
MandyProgzaAsked:
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ProculopsisCommented:
Take a look at this jsfiddle.

The code is:

$("#test").keyup(function() {
    var value = $(this).val().toUpperCase();
    value = value.replace(/[^0-9ST]/g, "");
    if ($(this).val() != value) $(this).val(value);
});

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MandyProgzaAuthor Commented:
Thanks, but what if I want to check if the first character is either S or T or 1?

Can you modify the code for that?
Atique AnsariCommented:
Above code does replace the code with blank value after accepting it. Its visible on screen that character is removed after being entered in text box.

Go to below URL.

http://jsfiddle.net/attu143/6pMeL/
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