How do I use req.flash() with EJS?

I know this is an old question, but I recently ran across it when trying to understand flash messages and templates myself, so I hope this helps others in my situation. Considering the case of Express 4, the express-flash module, and an ejs template, here are 2 routes and a template that should get you started.

First generate the flash message you want to display. Here the app.all() method maps to /express-flash. Request baseurl/express-flash to create a message using the req.flash(type, message) setter method before being redirected to baseurl/.

app.all('/express-flash', req, res ) {
  req.flash('success', 'This is a flash message using the express-flash module.');
  res.redirect(301, '/');
}

Next map the message to the template in the res.render() method of the target route, baseurl/. Here the req.flash(type) getter method returns the message or messages matching the type, success, which are mapped to the template variable, expressFlash.

app.get('/', req, res ) {
  res.render('index', {expressFlash: req.flash('success') });
}

Finally, display the value of expressFlash, if it exists, in index.ejs.

<p> Express-Flash Demo </p>    
<% if ( expressFlash.length > 0 ) { %>
  <p>Message: <%= expressFlash %> </p>
<% } %>

Then start the server and visit baseurl/express-flash. It should trigger a redirect to baseurl/ with the flash message. Now refresh baseurl/ and see the message disappear.

<% if ( message ) { %>
    <div class="flash"><%= message %></div>
<% } %>

Is this what you want? You can use some client-side JS to have it fading out. jQuery example:

var message = $( '.message' );
if ( message.length ) {
    setTimeout( function() {
        message.fadeOut( 'slow' );
    }, 5000 );
}

req.flash() can be used in two ways.

If you use two arguments

req.flash(type, message);

where type is a type of message and message is actual message (both strings), then it adds message to the queue of type type. Using it with one argument

req.flash(type);

returns array of all messages of type type and empties the queue. Additionally this method is attached to the session, so it works per session. In other words, each user has its own set of flash queues. So in your view you can do something like this:

var messages = req.flash('info');

and then send the messages variable to the template and use it there (note that messages is an array and you can iterate it). Remember that using req.flash('info', 'test'); will append a test message of type info only for a current user (associated with the req object).

Keep in mind that this mechanism is quite weak. For example if a user double clicks on link (two requests send to the server), then he will not see messages, because the first call will empty the queue (of course unless the request generates messages).

If you use visionmedia's express-messages helper module, it becomes very simple. Github link

As it says in the module's docs:

Install the module with npm

npm install express-messages

You then assign a dynamic helper for messages in the app.config:

app.dynamicHelpers({ messages: require('express-messages') });

In your EJS file, insert the following where you want your messages

<%- messages() %>

EJS renders this into:

<div id="messages">
  <ul class="info">
    <li>Email queued</li>
    <li>Email sent</li>
  </ul>
  <ul class="error">
    <li>Email delivery failed</li>
  </ul>
</div>

(of course, you can alter what it renders to in the module's code)

Then, to actually flash a message, include a call to:

req.flash('info', 'Your message goes here');