Node.js Web Apps With Express Using a Template Engine


Using a Template Engine

The following code will setup Jade as template engine. (Note: Jade has been renamed to pug as of December 2015.)

const express = require('express');  //Imports the express module
const app = express();  //Creates an instance of the express module

const PORT = 3000; //Randomly chosen port

app.set('view engine','jade'); //Sets jade as the View Engine / Template Engine
app.set('views','src/views'); //Sets the directory where all the views (.jade files) are stored.

//Creates a Root Route
app.get('/',function(req, res){
    res.render('index');  //renders the index.jade file into html and returns as a response. The render function optionally takes the data to pass to the view.

//Starts the Express server with a callback
app.listen(PORT, function(err) {
    if (!err) {
        console.log('Server is running at port', PORT);
    } else {

Similarly, other Template Engines could be used too such as Handlebars(hbs) or ejs. Remember to npm install the Template Engine too. For Handlebars we use hbs package, for Jade we have a jade package and for EJS, we have an ejs package.

EJS Template Example

With EJS (like other express templates), you can run server code and access your server variables from you HTML.
In EJS it's done using "<%" as start tag and "%>" as end tag, variables passed as the render params can be accessed using <%=var_name%>
For instance, if you have supplies array in your server code
you can loop over it using

<h1><%= title %></h1>
<% for(var i=0; i<supplies.length; i++) { %>
        <a href='supplies/<%= supplies[i] %>'>
            <%= supplies[i] %>
<% } %>

As you can see in the example every time you switch between server side code and HTML you need to close the current EJS tag and open a new one later, here we wanted to create li inside the for command so we needed to close our EJS tag at the end of the for and create new tag just for the curly brackets
another example
if we want to put input default version to be a variable from the server side we use <%=
for example:

<input type="text" value="<%= message %>" name="message" required>

Here the message variable passed from your server side will be the default value of your input, please be noticed that if you didn't pass message variable from your server side, EJS will throw an exception. You can pass parameters using res.render('index', {message: message}); (for ejs file called index.ejs).

In the EJS tags you can also use if , while or any other javascript command you want.