Backend Module Principles

For backend modules (that is, every module except the content area), we use the following guiding principles in addition to the already-existing principles:

  • It should be possible to write backend modules only with PHP, without JavaScript involved
  • Some features might be only available to the user if he has JavaScript enabled
  • In order to introduce rich behavior, use the technique of progressive enhancement

Progressive Enhancement

As we want to use progressive enhancement heavily, we need to define some rules as a basis for that.

First, you should always think about the non-javascript functionality, and develop the feature without JavaScript enabled. This helps to get the client-server communication function correctly.

For most parts, you should not rely at all on any server state, but instead use URI parameters to encode required state. This makes the server-side code a lot easier and progressive enhancement more predictable.

Furthermore, if you reload certain parts of the user interface using AJAX, make sure to always update the browser’s URI using History Management: In case there is an error, the user can just re-load the page and will get pretty much the same User Interface state. This fulfills our UI goal of “predictable UI behavior”.

Connecting JavaScript code to the HTML content

In order to connect JavaScript code to HTML content, we (of course) rely on CSS selectors for finding the correct DOM nodes. However, we do not want to use CSS class attributes, as they change more frequently. Instead, we’d like to use special data-attributes to connect the JavaScript code to the user interface.


In a nutshell:

  • CSS classes are used for the visible styling only
  • HTML5 Data Attributes are used for connecting the JavaScript code to HTML

We use the following data attributes for that:

  • data-area is used to search for DOM nodes, for later usage in JavaScript.

    As an example, use <div class="foo" data-area="actionBar"></div> in the HTML and match it using $('[data-area=actionBar]') in JavaScript.

  • data-json is used for transferring server-side state to the JavaScript as JSON.

    Example: We need the full URI parameters which have been used for the current rendering as array/object on the client side. Thus, the server side stores them inside <div style="display:none" data-json="uriParameters">{foo: 'bar'}</div>.

    The JavaScript code then accesses them at a central place using JSON.parse($('[data-json=uriParameters]').text()) and makes them available using some public API.

  • data-type is used to mark that certain parts of the website contain a client-side template language like handlebars.

    As an example for the action bar, we use the following code here:

         <span class="js" data-type="handlebars">
            {{#if multipleSelectionActive}} {{numberOfSelectedElements}} elements{{/if}}
    Then, on the client side in JavaScript, we use the handlebars template accordingly.

Adjusting the UI if JavaScript is (in-)active

Often, you want to hide or show some controls depending on whether JavaScript is enabled or disabled. By default, every DOM element is visible no matter whether JavaScript is enabled or not.

If you want to show a DOM element only if JavaScript is enabled, use the CSS class js.

If you want to show a DOM element only if JavaScript is disabled, use the CSS class nojs.