select dynamic textbox data

This is probably something simple I am missing.  I'm trying to create a validation checker for multiple elements.  I want to pass the element name into the function in javascript and if it doesn't pass the validation I want it to focus on the element and highlight the data in the element that is incorrect.  I want this done either onblur or onchange.

I haven't included all of the functions because the rest of it works.  In the javascript function the alert fires, but the focus and select do not.  it leaves the focus on the next element if you tab out or whatever element you click on next.

javascript:
function ValidateDate(varID)
{
alert('Please input a proper date with slashes');
var MyTextBox = document.getElementById(varID);
MyTextBox.focus();
MyTextBox.select();
///I've also tried this:
alert('Please input a proper date with slashes');
document.getElementById(varID).focus();
document.getElementById(varID).select();
}
 
HTML:
<form id="AddNewEmployeeform" >
    <input class="required" type="text" id="DateOfBirthTxt" name="DateOfBirthText" size="10" onchange="ValidateDate('DateOfBirthTxt');" />
</form>

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