Rendering Engine

How it works

Every page has an associated API call, Template file, and Language File.

For example, if you navigate to /topic/351/nodebb-wiki, the application will load three resources. The API return /api/topic/351/nodebb-wiki and the template, in this example, “topic.tpl”, and the appropriate language file “topic.json”*.

Just prepend api/ to the URL’s path name to discover the JSON return. Any value in that return can be utilized in your template.

*A page’s name corresponds to the template and language’s filename (ex. http://domain.com/topic/xyz correlates to topic.tpl).

Templating Basics

Using the API return as your guide, you can utilize any of those values in your template/logic. Using the above API call as an example, for anything in the root level of the return you can do something like:

{topic_name}

To access values in objects:

{privileges.read}

And finally you can loop through arrays and create blocks like so:

<!-- BEGIN posts -->
{posts.content}
<!-- END posts -->

The above will create X copies of the above block, for each item in the posts array.

Templating Logic

NodeBB’s templating system implements some basic logic. Using the same API call as above for our example. You can write IF conditionals like so:

<!-- IF unreplied -->
This thread is unreplied!
<!-- ENDIF unreplied -->

Another example:

<!-- IF !disableSocialButtons -->
<button>Share on Facebook</button>
<!-- ELSE -->
Sharing has been disabled.
<!-- ENDIF !disableSocialButtons -->

We can check for the length of an array like so:

<!-- IF posts.length -->
There be some posts
<!-- ENDIF posts.length -->

While looping through an array, we can check if our current index is the @first or @last like so:

<!-- BEGIN posts -->
  <!-- IF @first -->
    <h1>Main Author: {posts.username}</h1>
  <!-- ENDIF @first -->
  {posts.content}
  <!-- IF @last -->
    End of posts. Click here to scroll to the top.
  <!-- ENDIF @last -->
<!-- END posts -->

For more advanced documentation, have a look at the templates.js repository

Exposing template variables to client-side JavaScript

There are two ways of letting our JS know about data from the server-side, apart from WebSockets (TODO: will be covered in a different article).

Via jQuery.get

If we require data from a different page we can make a $.get call to any other API call. For example, if we wanted to know more about a specific user we could make a call like so:

$.get(RELATIVE_PATH + '/api/user/psychobunny', {}, function(user) {
    console.log(user)
});

See this API call in action: http://community.nodebb.org/api/user/psychobunny

Via Template Variables

In topic.tpl for example, we can add a hidden input like so:

<input type="hidden" template-variable="pageCount" value="{pageCount}" />

The template system will immediately parse all of these and expose them via the following method:

ajaxify.variables.get('pageCount');

This is the ideal method of letting JS know about important variables within the template.

Internationalization

The template engine interfaces with the internationalization system as well. We can embed variables into language strings. Let’s use this API call as well as this language file as an example. We can now do something like the following:

[[register:help.username_restrictions, {minimumUsernameLength}, {maximumUsernameLength}]]

Which will translate this string:

A unique username between %1 and %2 characters

to

A unique username between 2 and 16 characters

Advanced Topics

Dynamically requiring and rendering a template file from client-side JavaScript

The template engine lazy loads templates on an as-needed basis and caches them. If your code requires a template or partial on-demand then you can :

ajaxify.loadTemplate('myTemplate', function(myTemplate) {
        var html = templates.parse(myTemplate, myData);
});

You can also access the invidual blocks inside each template, which is handy for doing things like (for example) rendering a new post’s <li> and dynamically sticking it in an already loaded <ul>

Some stuff here...
<!-- BEGIN posts -->
We just want to pull this block only.
<!-- END posts -->
... some stuff here
ajaxify.loadTemplate('myTemplate', function(myTemplate) {
        var block = templates.getBlock(myTemplate, 'posts');
        var html = templates.parse(block, myData);
});

Rendering templates on server-side Node.js

The templating system hooks into Express just like most other templating frameworks. Just use either app.render or res.render to parse the appropriate template.

res.render('myTemplate', myData);
app.render('myTemplate', myData, function(err, parsedTemplate) {
        console.log(parsedTemplate);
});