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Asyncronous Embedded JavaScript Templates with Q

Build Status # Asyncronous Embedded JavaScript Templates with Q


This library impliments Embedded JavaScript with some asyncronous additions provided by Q. It is broadly based on and fully supports everything except filters. For a full discussion of the reasoning behind this, see Features below. The promises implimentation for ayncronous operations uses so you'll need to make sure that all asyncronous functions/values you supply to the templates are 'thenables' so that they'll work with Q. All that means in practice is that you need your promises to have a function then that you can call with a promise.


$ npm install qejs


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


qejs.compile(str, options);
// => Function

qejs.render(str, options);
// => promise

qejs.render(str, options).then(function(output){
        //output is a string


  • cache Compiled functions are cached, requires filename
  • filename Used by cache to key caches
  • scope Function execution context
  • debug Output generated function body
  • open Open tag, defaulting to "<%"
  • close Closing tag, defaulting to "%>"
    •             All others are template-local variables

Custom tags

Custom tags can also be applied globally:

var qejs = require('qejs'); = '{{';
qejs.close = '}}';

Which would make the following a valid template:

<h1>{{= title }}</h1>

Unbuffered Code

<% code %>

QEJS supports exactly the same syntax as EJS for unbuffered code, usefull for conditionals, loops etc.

Escapes HTML

<%= code %>

This differs from EJS in that if code returns a promise, it is resolved and then escaped before being outputted. While this is happening, QEJS will continue on to render the rest of the template, allowing many promised functions to be executed in parallel.

Unescaped Buffering

<%- code %>

If code isn't a promise, this will work exactly like EJS, but if code is a promise, we will resolve it, before outputting the resolved value. We won't do any escaping on this value, so only use for trusted values, not user input.

Async Blocks

<% promise -> value %>...Use value here...<% <- %>
<% PromiseForAnArray -> [valueA, valueB, valueC...] %>...Use values individually here...<% <- %>
<% [promiseA,promiseB,promiseC...] -> values %>...Use identifier as an array of resolved values...<% <- %>
<% [promiseA,promiseB,promiseC...] -> [valueA,valueB,valueC...] %>...Use values individually here...<% <- %>

Async blocks are considered a relatively advanced feature, and where possible you should try and tick to just returning promises through <%= code %> as it's much easier to write that without creating bugs.

Having said that, async blocks are not difficult to write and I hope you'll end up really loving them for those times when you really need them.

What happens in an async block is we reserve a space for whatever text is outputted by the block, allowing you to use any QEJS inside the async block (including another async block). We then resolve the value of the promise you give us, and we give it the name you specify on the right hand side of the arrow operator. The async block starter must go in its own separate unbuffered code block, but you could put other things like comments inside the block with the end marker.

Once you go past the end marker of an async block, you will no longer have access to the value of the promise. This lets us run lots of calls in parallel, and means that you can use async blocks inside if statments, for statements, while statements, function statements, pretty much anywhere you could write regular EJS.

Inheritance and Partials

QEJS supports both inheritance and partials. Inheritance is used to include the current template in the middle of some other template (similar to express's layout templates except a little more powerful). Currently this only works if you use the renderFile method (or render in express with the following snippet to setup).


Inheritance allows you to support features similar to those in express's layout template. To use a layout for a template, simply call inherits('relative/path/to/template') anywhere in your template that is not run asyncronously. That is to say, it can't go inside an async block, or inside the then callback of a promise. Usually it's best to put it at the top of your file. If you call it multiple times, it will throw an exception.


<% inherits('layouts/navigation') %>
<p>The great page foobar</p>


<% inherits('base') %>
<a href="#home">Home</a>
<a href="#about">About</a>
<div class="content">
    <%- contents %>


<!DOCTYPE html>
<html lang="en">
        <meta charset="utf-8">
        <%- contents %>

Be careful not to inherit from yourself as this would create errors that never got caught if you create an infinite loop of inheritance.

As you can see, paths are resolved in a very forgiving way. They are resolved relative to the current file, then relative to the parent directory of the current directory and so on up the tree until a file is found. It will try for files with extensions '.qejs', '.ejs' and '.html' in that order unless you specify an extension.


You can render a child template within the current template. By default, it does not currently have access to any local variables of the calling template, only those supplied in options.

To use, simply call render anywhere in the parent template.


<!DOCTYPE html>
<html lang="en">
        <meta charset="utf-8">
        <%- render('views/foobar', {message:'hello world'}) %>
<p><%= message %></p>

Newline slurping

If you end any code block with a - even if it's an async block, we'll support newline slurping for you (<% code -%> or <% -%> or <%= code -%>, <%- code -%>, <% promise -> result -%> or <% < -%>) That is to say, we won't output the next new line after we see that symbol. QEJS never outputs a newline inside a code block.


QEJS doesn't support filters. Although in a way it seems a shame not to maintain 100% compatability with the syncronous form of EJS, I think that it's more important to keep this library lean. Filters don't really add a lot, you can always attach such methods to arrays yourself and use standard javascript syntax, I don't want to hurt the purity of EJS though, so I've chosen not to add this syntax (bloat).

ExpressJS Integration

This module is fully compatible with express 3.0.0 via the consolidate.js library.

To use it you'll need to install both consolidate and QEJS. You can do this in a single command with:

npm install consolidate qejs

The following example demonstrates using QEJS in express:

var express = require('express')
  , cons = require('consolidate')
  , app = express();
// assign the swig engine to .html files 
app.engine('html', cons.qejs);
// set .html as the default extension  
app.set('view engine', 'html');
app.set('views', __dirname + '/views');
var users = [];
users.push({ name: 'tobi' });
users.push({ name: 'loki' });
users.push({ name: 'jane' });
app.get('/', function(req, res){
  res.render('index', {
    title: 'Consolidate.js'
app.get('/users', function(req, res){
  res.render('users', {
    title: 'Users',
    users: users
console.log('Express server listening on port 3000');

If it doesn't work, be sure to make absolutely certain you've got the latest version of express, and make sure you have actually created a users.html and index.html view.


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