title: Push notification for error email/password checking using nodejs
body: <p>I am using nodeJS and express to create a simple log in form where user need to put their email and password to log in. 
  For example, in client side:</p>
  
  <pre><code>  form(action='/login', method='post')
        .form-group
          label Email
          input.form-control(type='text', name='email')
          span#message
        .form-group
          label Password
          input.form-control(type='password', name='password')
        button.btn.btn-warning.btn-lg(type='submit') Login
  </code></pre>
  
  <p>In server side:</p>
  
  <pre><code>router.get('/', function(req, res, next) {
  res.render('index', { title: 'Login' });
  
  // process the login form
  router.post('/login', function(req, res){
      if(req.body.email &amp;&amp; req.body.password == 'pass123') {
          res.redirect('/myHomePage);
      }else {
          res.redirect('/');
      }
   });
  </code></pre>
  
  <p>My question is, how can I check if user is enter the valid email and valid password (which declared in server-side (pass123)). How can I have a popup/ or a message on client side to tell user that they input the wrong username/password.</p>
  
  <p>I am not using any database at the moment.  </p>