Email validation using Javascript

function EmailValidCheck(emailtxt)
{
 var email1=document.getElementById(emailtxt).value;
 var emailfilter=/^\w+[\+\.\w-]*@([\w-]+\.)*\w+[\w-]*\.([a-z]{2,4}|\d+)$/i;
 if(email1.length>0)
 {
 var returnval=emailfilter.test(email1);
 if (returnval==false)
 {
 alert("Please Enter Valid Employee Email ID !!")
 document.getElementById(emailtxt).focus();
 return false;
 }
 }
}