A template engine enables you to use static template files in your application. At runtime, the template engine replaces variables in a template file with actual values, and transforms the template into an HTML file sent to the client. This approach makes it easier to design an HTML page.

Some popular template engines that work with Express are Pug, Mustache, and EJS. The Express Application Genreator uses Jade as its default, but it also supports several others.

After the view engine is set, you don’t have to specify the engine or load the template engine module in your app; Express loads the module internally, as shown below (for the above example).

app.set('view engine', 'pug')

Create a Pug template file named index.pug in the views directory, with the following content:

html
  head
    title= title
  body
    h1= message

Then create a route to render the index.pug file. If the view engine property is not set, you must specify the extension of the view file. Otherwise, you can omit it.

app.get('/', (req, res) => {
  res.render('index', { title: 'Hey', message: 'Hello there!' })
})

When you make a request to the home page, the index.pug file will be rendered as HTML.

Note: The view engine cache does not cache the contents of the template’s output, only the underlying template itself. The view is still re-rendered with every request even when the cache is on.