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$(document).ready(function () {
  //called when key is pressed in textbox
  $("#js-cc_number input").keypress(function (e) {
     //if the letter is not digit then display error and don't type anything
     if (e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57)) {
        //display error message
        $("#errmsg").html("Digits Only").show().fadeOut("slow");
               return false;
    }
   });
});