mde/ejs

Embedded JavaScript templates

Security

Security professionals, before reporting any security issues, please reference the SECURITY.md in this project, in particular, the following: "EJS is effectively a JavaScript runtime. Its entire job is to execute JavaScript. If you run the EJS render method without checking the inputs yourself, you are responsible for the results."

In short, DO NOT submit 'vulnerabilities' that include this snippet of code:

app.get('/', (req, res) => {
  res.render('index', req.query);
});

Installation

$ npm install ejs

Import or require

Supports both CommonJS and ES Modules.

import ejs from 'ejs';
// Or
const ejs = require('ejs');

Compatibility

Server: CommonJS approach (require) supports Node versions at least back to v0.12, likely older versions too. ES Modules approach (import) requires a Node version that supports ESM.

CLI: Requires Node v8 or newer.

Browser: EJS supports all modern browsers, but is very likely to work even in very, very old browsers. Your mileage may vary.

Bundlers and alternate runtimes: as of v6.0, the published package imports cleanly under Rollup, Rolldown, tsdown, esbuild, Webpack, Vite, Browserify, Bun, and Deno. Earlier versions emitted module.exports = ejs; from inside the ESM source as a dual-mode shim; modern ESM-aware bundlers and Bun treated this as malformed ESM. The shim has been removed from lib/esm/*.js and moved into the lib/cjs/* compile step, so the published CJS surface (require('ejs')) is unchanged. For Browserify, pass --node so it picks the main entry instead of the prebuilt UMD bundle pointed to by the browser field.

Browser-targeted bundlers that support conditional exports select the prebuilt bundle through the browser export condition. Use this bundle to compile and render template strings; loading templates from the filesystem with renderFile requires the Node entry point.

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 surrounding spaces and tabs) 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

Example

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

Basic usage

const template = ejs.compile(str, options);
template(data);
// => Rendered HTML string

ejs.render(str, data, options);
// => Rendered HTML string

ejs.renderFile(filename, data, options, function(err, str){
    // str => Rendered HTML string
});

Important

You should never give end-users unfettered access to the EJS render method, If you do so you are using EJS in an inherently un-secure way.

Options

• cache Compiled functions are cached, requires filename
• filename The name of the file being rendered. Not required if you are using renderFile(). Used by cache to key caches, and for includes.
• root Set template root(s) for includes with an absolute path (e.g, /file.ejs). Can be array to try to resolve include from multiple directories.
• views An array of paths to use when resolving includes with relative paths.
• context Function execution context
• compileDebug When false no debug instrumentation is compiled
• delimiter Character to use for inner delimiter, by default '%'
• openDelimiter Character to use for opening delimiter, by default '<'
• closeDelimiter Character to use for closing delimiter, by default '>'
• debug Outputs generated function body
• strict When set to true, generated function is in strict mode
• _with Whether or not to use with() {} constructs. If false then the locals will be stored in the locals object. Set to false in strict mode.
• unsafePrototypeLocals When true, allows templates to resolve identifiers through the prototype chain of the locals object. Required if you pass class instances or Object.create(...) results as locals and rely on inherited properties at the top level. Defaults to false; enabling it disables the v6 prototype-pollution mitigation.
• destructuredLocals An array of local variables that are always destructured from the locals object, available even in strict mode.
• localsName Name to use for the object storing local variables when not using with Defaults to locals
• rmWhitespace Remove all safe-to-remove whitespace: leading and trailing whitespace on each line, and blank lines. Because trailing spaces are removed first, -%> reliably trims the newline after a tag.
• escape The escaping function used with <%= construct. (By default escapes XML.) See Escaping and output context for when the default is not the right choice.
• outputFunctionName Set to a string (e.g., 'echo' or 'print') for a function to print output inside scriptlet tags.
• async When true, EJS will use an async function for rendering. (Depends on async/await support in the JS runtime).
• includer Custom function to handle EJS includes, receives (originalPath, parsedPath) parameters, where originalPath is the path in include as-is and parsedPath is the previously resolved path. Should return an object { filename, template }, you may return only one of the properties, where filename is the final parsed path and template is the included content.

This project uses JSDoc. For the full public API documentation, clone the repository and run jake doc. This will run JSDoc with the proper options and output the documentation to out/. If you want the both the public & private API docs, run jake devdoc instead.

Tags

• <% 'Scriptlet' tag, for control-flow, no output
• <%_ 'Whitespace Slurping' Scriptlet tag, strips spaces and tabs 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 a newline directly after it
• _%> 'Whitespace Slurping' ending tag, removes spaces and tabs after it, then one newline

Escaping and output context

1. EJS is most often used to generate HTML.
2. <%= %> reflects that. It escapes for HTML content and quoted attribute values.
3. EJS also generates arbitrary strings for other contexts, and knows nothing about where its output ends up.
4. You can replace the default escaping.
5. Outside HTML content, you should.

ejs.render(template, data, {escape: myEscapeFunction});

escape must go in the options argument. It cannot be set on ejs globally or passed in with the data. For a template that mixes contexts, escape per value with <%- myEscapeFunction(name) %> instead.

The usual mistake is <%= %> inside a <script> block. Browsers do not decode HTML entities there, so the default escaping neither renders correctly nor protects you. Pass the value through an attribute and JSON.parse it instead of splicing it into JavaScript source. (JSON.stringify output is not safe there either. A </script> anywhere in your data ends the block early.)

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:

import ejs from 'ejs';
const 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:

import ejs from 'ejs';
import { LRUCache } from 'lru-cache';

ejs.cache = LRUCache({max: 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.

import ejs from 'ejs';

const 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') -%>

Client-side support

Go to the Latest Release, download ./ejs.js or ./ejs.min.js. Alternately, you can compile it yourself by cloning the repository and running jake build (or npx jake build if jake is not installed globally).

Include one of these files on your page, and ejs should be available globally.

Example

<div id="output"></div>
<script src="ejs.min.js"></script>
<script>
  let people = ['geddy', 'neil', 'alex'],
      html = ejs.render('<%= people.join(", "); %>', {people: people});
  // With jQuery:
  $('#output').html(html);
  // Vanilla JS:
  document.getElementById('output').innerHTML = html;
</script>

Caveats

Most of EJS will work as expected; however, there are a few things to note:

1. Obviously, since you do not have access to the filesystem, ejs.renderFile() won't work.
2. For the same reason, includes do not work unless you use an include callback. Here is an example:

let str = "Hello <%= include('file', {person: 'John'}); %>",
    fn = ejs.compile(str);

fn(data, null, function(path, d){ // include callback
  // path -> 'file'
  // d -> {person: 'John'}
  // Put your code here
  // Return the contents of file as a string
}); // returns rendered string

See the examples folder for more details.

CLI

EJS ships with a full-featured CLI. Options are similar to those used in JavaScript code:

• -o / --output-file FILE Write the rendered output to FILE rather than stdout.
• -f / --data-file FILE Must be JSON-formatted. Use parsed input from FILE as data for rendering.
• -i / --data-input STRING Must be JSON-formatted and URI-encoded. Use parsed input from STRING as data for rendering.
• -m / --delimiter CHARACTER Use CHARACTER with angle brackets for open/close (defaults to %).
• -p / --open-delimiter CHARACTER Use CHARACTER instead of left angle bracket to open.
• -c / --close-delimiter CHARACTER Use CHARACTER instead of right angle bracket to close.
• -s / --strict Generate the function in strict mode (implies --no-with).
• -n / --no-with Use 'locals' object for vars rather than using with.
• -l / --locals-name NAME Name to use for the object storing local variables when not using with.
• -w / --rm-whitespace Remove all safe-to-remove whitespace, including leading and trailing whitespace.
• -d / --debug Outputs generated function body
• -h / --help Display this help message.
• -V/v / --version Display the EJS version.

Here are some examples of usage:

$ ejs -p [ -c ] ./template_file.ejs -o ./output.html
$ ejs -m $ ./test/fixtures/user.ejs name=Lerxst
$ ejs -n -l _ ./some_template.ejs -f ./data_file.json

Arguments

As of v7:

• The template file comes first. Any name=value data comes after it.
• Unknown options are an error.
• Short options can be grouped (-sdw) and take attached values (-m$).
• A value that starts with - needs =: -o=-out.html.
• -- ends options, for example when a template's name starts with -.
• Exit status is 0 on success, 2 for a usage error, and 1 for a runtime error.

Data input

Pass JSON data one way: stdin, a data file (-f), or a command-line option (-i). Using -f and -i together is an error. Stdin is only read when there's no -f, -i, or name=value data.

Stdin:

$ cat ./test/fixtures/user_data.json | ejs -m $ ./test/fixtures/user.ejs
$ ejs -m $ ./test/fixtures/user.ejs < test/fixtures/user_data.json

A data file:

$ ejs -m $ ./test/fixtures/user.ejs -f ./test/fixtures/user_data.json

A command-line option (must be URI-encoded):

./bin/cli.js -m $ -i %7B%22name%22%3A%20%22foo%22%7D ./test/fixtures/user.ejs

Or, passing name=value pairs after the template. These override values from -f or -i, and are always strings:

./bin/cli.js -m $ ./test/fixtures/user.ejs name=foo

Output

The CLI sends output to stdout by default. Use -o or --output-file to write it to a file instead.

IDE Integration with Syntax Highlighting

VSCode:Javascript EJS by DigitalBrainstem

Related projects

There are a number of implementations of EJS:

• TJ's implementation, the v1 of this library: https://github.com/tj/ejs
• EJS Embedded JavaScript Framework on Google Code: https://code.google.com/p/embeddedjavascript/
• Sam Stephenson's Ruby implementation: https://rubygems.org/gems/ejs
• Erubis, an ERB implementation which also runs JavaScript: http://www.kuwata-lab.com/erubis/users-guide.04.html#lang-javascript
• DigitalBrainstem EJS Language support: https://github.com/Digitalbrainstem/ejs-grammar

License

Licensed under the Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)

EJS Embedded JavaScript templates copyright 2112 [email protected].