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Managing Client-side Templates with RequireJS

Sunday, July 15th, 2012

When developing single page web applications, patterns of structure, organization and reuse become ever more important. This especially holds true when there is a need to maintain mulitiple web applications, each of which targeting a specific form factor, while also sharing many of the same underlying core APIs.

In the context of client-side templating, such patterns begin to emerge, quite naturally so, when leveraging RequireJS modules and the RequireJS text plugin.

Template Modules

One specific pattern I have found myself implementing is that of a single Templates Module which provides a centralized location from which all compiled templates within an application can be referenced. A rather simple pattern, Template Modules are only concerned with loading, compiling and providing a public API to access compiled templates; that is, a Templates Module simply requires all external templates, and provides named methods for retrieving the compiled template functions of each.

A basic implementation of a Templates module is as follows (while Handlebars may be used in this example, any template engine would suffice):

The main benefit of implementing a Templates Module is reuse, as different modules can use the same templates without a need for redundantly requiring and compiling the templates themselves. Additionally, Template Modules provide a convenient means of abstracting away the underlying template engine from client code, thus reducing the amount of refactoring needed should the template engine itself ever need to change.

When using the RequireJS Optimizer, each external template will be included in the optomized build and loaded synchronously, and so there is no additional overhead in terms of HTTP requests when requiring each template in a single location.

You can check out a basic example implementation of a Templates Module (in the context of Backbone) here.

Testing Handlebars Helpers with Jasmine

Tuesday, March 13th, 2012

For some time now, I have primarily been using logic-less templating solutions as they allow for a greater separation of concerns in comparison to many of their logic-based counterparts. By design, the decoupling of logic-less templates imparts greater overall maintainability in that templates become considerably less complex, and therefore, considerably easier to maintain and test.

Handlebars, my preferred logic-less templating engine, simplifies testing even further via it’s elegant Helper API. While Handlebars may not be the fastest templating solution available, I have found it to be the most testable, reusable and thus, maintainable.

Custom Handlebars Helpers

Since Handlebars is a logic-less templating engine, the interpolation of values which require logical operations and/or computed values is facilitated via Helpers. This design is quite nice in that template logic can be tested in isolation from the context in which it is used; i.e. the templates themselves. In addition to the common built-in Block Helpers, custom Helpers can easily be registering in order to encapsulate the logic used by your templates.

Registering Custom Helpers

Registering Custom Helpers is as simple as invoking Handlebars.registerHelper; passing the string name of the helper which is to be registered, followed by a callback which defines the actual helpers implementation.

Consider the following custom Helper example, which, given a string of text, replaces plain-text URLs with anchor tags:


As can be seen in the above example, custom Handlebars Helpers are registered outside the context of the templates in which they are used. This allows us to test our custom Helpers quite easily.

Testing Custom Helpers

Generally, I prefer to abstract testing custom Helpers specifically, and test the actual templates which use the Helpers independently from the Helpers. This allows for greater portability as it promotes reuse in that common custom Helpers (and their associated tests) can then be used across multiple projects, regardless of the templates which use them. While one can test Handlebars implementation code with any testing framework, in this example I will be using Jasmine.

Essentially, testing Custom Helpers is much the same as testing any other method. The only point to be noted is that we first need to reference the helper from the Handlebars.helpers namespace. Ideally this could be avoided as, should the namespace happen to change, so, too, will our tests need to change. That being said, the probability of such a change is unlikely.

Using the above example, in a Jasmine spec, the enhance helper can be referenced as follows:

Then we can test that the helper was registered:

We can then test any expectation. For example, the enhance helper should return a Handlebars.SafeString. We can test this as follows:

The enhance helper is expected to replace plain-text URLs with anchor tags. Before testing this, though, we should first test that it preserves existing markup. In order to test this use-case, we first need to access the return value from our custom Helper, we can do this by referencing the string property of the Handlebars.SafeString returned by our Helper:

Finally, we test that our enhance Helper replaces URLs with anchor tags using the above techniques:


We now have a complete test against our custom Helper, and all is green:
Custom Helper Spec
Note: The above Spec Runner is using the very nice jasmine.BootstrapReporter

And that’s all there is to it. You can fork the example at handlebars-helpers-jasmine.

Integrating Handlebars Templates in Kendo UI

Monday, March 5th, 2012

I have been evaluating Kendo UI recently for its rich set of Widget APIs and general HTML5 UI Framework capabilities. One of the first things I wanted to see was how easily Kendo UI Widgets could be integrated with different Templating Engines, Handlebars in particular.

By default, Kendo UI provides out of the box templating support via Kendo UI Templates as well as support for jQuery Templates. While both solutions are quite good, I generally prefer logic-less Templating, with Handlebars being my preferred Template Engine of choice.

Fortunately, as it turns out, integration with Handlebars is actually quite simple. In fact, integration with basically any Template Engine is rather straight forward and can be implemented transparently.


In order to use a Template Engine which is not supported by default, one just needs to implement a Widget’s specific template property as a method which returns the resulting markup from a compiled template. This is easiest to understand by viewing examples in the context of both default templating as well as specific template integration.

First, templates in Kendo UI are typically implemented as follows (with this particular example being in the context of the rowTemplate of the Kendo UI Grid):

Note that in the above example the compiled template is directly assigned to the rowTemplate property.

Now, to integrate a Template Engine of your choosing (in this example, Handlebars), assign a function to the rowTemplate property. The function assigned accepts a data object (which represents the data of a row) and, simply invoke the complied template with the data object, returning the result as follows:

And thats all there is to it. You can try the above example implementation here.

External Templates in jQote2

Monday, December 12th, 2011

The jQote2 API Reference provides plenty of useful examples which are sure to help users get up and running quickly. I found it a bit unclear, though, as to how templates could be loaded externally as, in the reference examples, templates are defined within the containing page. For the sake of simplicity this approach certainly makes sense in the context of examples. However, in practice, templates would ideally be loaded externally.

While jQote2 provides a perfect API for templating, it does not provide a method specifically for loading external templates; this is likely due to the fact that loading external templates could easily be accomplished natively in jQuery. However, since this is a rather common development use case, having such a facility available would be quite useful.

After reviewing the comments I came across a nice example from aefxx (the author of jQote2) which demonstrated a typical approach to loading external templates which was simular to what I had been implementing myself.

And so, I wrote a simple jQuery Plug-in which provides a tested, reusable solution for loading external templates. After having leveraged the Plugin on quite a few different projects, I decided to open source it as others may find it useful as well.

Using the Plugin

Using the jQote2 Template Loader plugin is rather straight forward. Simply include jQuery, jQote2 and the jquery.jqote2.loader-min.js script on your page.

As a basic example, assume a file named example.tpl exists, which contains the following template definition:

We can load the example.tpl template file described above via $.jqoteload as follows:

After example.tpl has been loaded, from another context we can access the compiled templates via their template element id. In this example "articles_tpl".

You can grab the source and view the example over on the jQote2 Template Loader Github page.