HTML Form - email validation

In HTML Form - Email validation in javascript here are the steps  its easy to do email validation in javascript

JavaScript code to validate an email id

var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;

if (!filter.test(mail)) {
    alert('Please provide a valid email address');
    email.focus;
    return false;
  }