Validate email address in JS

Following java script function can be used to check email validation.

function checkEmail() {        

var email = document.getElementById('txtEmail');      

  var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;        
   if (!filter.test(email.value)) {      
   alert('Please provide a valid email address');      
   email.focus;      
   return false;   
}