SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<input name="TextBox1" type="text" id="TextBox1" />
<span id="RequiredFieldValidator1" style="color:Red;visibility:hidden;">RequiredFieldValidator</span>
<span id="RegularExpressionValidator1"></span>

<input type="submit" name="Button1" value="Button" onclick="javascript:WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions(&quot;Button1&quot;, &quot;&quot;, true, &quot;&quot;, &quot;&quot;, false, false))" id="Button1" />
<input type="button" value="Test" onclick="ml_test();" />

<script type="text/javascript">
    ml_test = function() {
        alert($('span:validatorFor(TextBox1)').length);
    };
</script>
<script type="text/javascript">
//<![CDATA[
var RequiredFieldValidator1 = document.all ? document.all["RequiredFieldValidator1"] : document.getElementById("RequiredFieldValidator1");
RequiredFieldValidator1.controltovalidate = "TextBox1";
RequiredFieldValidator1.errormessage = "RequiredFieldValidator";
RequiredFieldValidator1.evaluationfunction = "RequiredFieldValidatorEvaluateIsValid";
RequiredFieldValidator1.initialvalue = "";
//]]>
</script>

JavaScript

jQuery.expr[':'].validatorFor = function(o, i, m){
  return o.controltovalidate === m[3];
};