// Get the field that fired the event.
var oField = event.srcElement;
// Validate the field information.
if (typeof(oField) != "undefined" && oField.DataValue != null)
{
// Remove any non-numeric characters.
var sTmp = oField.DataValue.replace(/[^0-9]/g, "");
// If the number has a valid length, format the number.
switch (sTmp.length)
{
case "4105551212".length:
oField.DataValue = "(" + sTmp.substr(0, 3) + ") " + sTmp.substr(3, 3) + "-" + sTmp.substr(6, 4);
break;
case "5551212".length:
oField.DataValue = sTmp.substr(0, 3) + "-" + sTmp.substr(3, 4);
break;
}
}