Templating (EJS)

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Template Engines

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.

Installation

npm install ejs

Features of EJS

• Features
• Control flow with <% %>
• Escaped output with <%= %> (escape function configurable)
• Unescaped raw output with <%- %>
• Newline-trim mode (‘newline slurping’) with -%> ending tag
• Whitespace-trim mode (slurp all whitespace) for control flow with <%_ _%>
• Custom delimiters (e.g. [? ?] instead of <% %>)
• Includes
• Client-side support
• Static caching of intermediate JavaScript
• Static caching of templates
• Complies with the Express view system

A Simple Example

<% if (user) { %>
  <h2><%= user.name %></h2>
<% } %>

Try EJS online at: https://ionicabizau.github.io/ejs-playground/.

Tags

• <% ‘Scriptlet’ tag, for control-flow, no output
• <%_ ‘Whitespace Slurping’ Scriptlet tag, strips all whitespace before it
• <%= Outputs the value into the template (escaped)
• <%- Outputs the unescaped value into the template
• <%\# Comment tag, no execution, no output
• <%% Outputs a literal ‘<%’
• %%> Outputs a literal ‘%>’
• %> Plain ending tag
• -%> Trim-mode (‘newline slurp’) tag, trims following newline
• _%> ‘Whitespace Slurping’ ending tag, removes all whitespace after it

Includes

Includes either have to be an absolute path, or, if not, are assumed as relative to the template with the include call. For example if you are including ./views/user/show.ejs from ./views/users.ejs you would use <%- include(‘user/show’) %>.

You must specify the filename option for the template with the include call unless you are using renderFile().

You’ll likely want to use the raw output tag (<%-) with your include to avoid double-escaping the HTML output.

<ul>
  <% users.forEach(function(user){ %>
    <%- include('user/show', {user: user}) %>
  <% }); %>
</ul>

Includes are inserted at runtime, so you can use variables for the path in the include call (for example <%- include(somePath) %>). Variables in your top-level data object are available to all your includes, but local variables need to be passed down.

NOTE: Include preprocessor directives (<% include user/show %>) are not supported in v3.0+.

Custom delimiters

Custom delimiters can be applied on a per-template basis, or globally:

const ejs = require('ejs'),
      users = ['geddy', 'neil', 'alex'];
 
// Just one template
ejs.render('<p>[?= users.join(" | "); ?]</p>', {users: users}, {delimiter: '?', openDelimiter: '[', closeDelimiter: ']'});
// => '<p>geddy | neil | alex</p>'
 
// Or globally
ejs.delimiter = '?';
ejs.openDelimiter = '[';
ejs.closeDelimiter = ']';
ejs.render('<p>[?= users.join(" | "); ?]</p>', {users: users});
// => '<p>geddy | neil | alex</p>'

Caching

EJS ships with a basic in-process cache for caching the intermediate JavaScript functions used to render templates. It’s easy to plug in LRU caching using Node’s lru-cache library:

let ejs = require('ejs'),
    LRU = require('lru-cache');
ejs.cache = LRU(100); // LRU cache with 100-item limit

If you want to clear the EJS cache, call ejs.clearCache. If you’re using the LRU cache and need a different limit, simple reset ejs.cache to a new instance of the LRU.

Custom file loader

The default file loader is fs.readFileSync, if you want to customize it, you can set ejs.fileLoader.

let ejs = require('ejs');
let myFileLoad = function (filePath) {
  return 'myFileLoad: ' + fs.readFileSync(filePath);
};
 
ejs.fileLoader = myFileLoad;

With this feature, you can preprocess the template before reading it.

Layouts

EJS does not specifically support blocks, but layouts can be implemented by including headers and footers, like so:

<%- include('header') -%>
<h1>
  Title
</h1>
<p>
  My page
</p>
<%- include('footer') -%>