RequiredFieldValidator ennable with javascript

Question

 function Validation() 

{

 if (document.Form1.txtfrom2.value.length > 0)

 ValidatorEnable(Rftxtfrom2, true); 

 ValidatorEnable(Rftxtjd2, true); 

 ValidatorEnable(Rftxtflno2, true); 

 ValidatorEnable(Rftxtdep2, true); 

 

} 

</script>
i need to txtfrom2 text box contain 1 charecter 4 RequiredFieldValidator automaticaly ennable true